Grand Prix Seats are interchangeable with Trans Am Deluxe Seats

The roof in my Bandit Trans Am leaks, so my seat frames and buns were in terrible shape. I bought a 76 Grand Prix to get some more seat buns. I bought this car sight unseen, but the Lord was looking out for me: the seats were very lightly used. Whoever owned this car didn't weigh much!

This page shows PUI Trans Am upholstery in 1977 Buckskin being applied on Grand Prix seat frames and buns. It also shows which parts are interchangeable left to right.

Side By Side Comparison
Grand Prix on the left, Trans Am on the right. That's not the original Trans Am upholstery, but that is original Buckskin Perf on the left. The difference in condition of frames and buns is pretty evident.
Two things to note:

The grand prix seat is jacked up by its tall tracks

The original trim panel can be seen at the bottom left, still in place.

This height difference, purely accomplished by tracks, seems to have given people the idea that the seats are different. This prevented the Trans Am seat covers from being sold as Grand Prix seat covers up to now. Seats!

Seat Frame
Here's the Grand Prix Seat Frame. It is still shiny after 25 years. Wow! My Trans Am seat frame is ashamed to get in the picture for comparison. That light stuff you see is actual shiny metal! None of the wires are broken! Eat your heart out.
This frame is interchangeable for left and right seats.
Frame

Seat Bun
This is the Grand Prix Seat Bun. It's in great shape. The part number is 9875139. According to the parts catalog it was used in A, G, X, and F bodies with custom interior. This is the driver's side cushion, but left and right are interchangeable. If you can't find a good driver's seat, you can start with two passenger seats and build one of them into a driver's seat.
You'll note that this seat bun is designed for a "horsecollar". It was not changed from the 1973 upholstery. That means that all 73-77 Grand Prix seat buns would interchange. You can tell from the stripes that it was a 76-77 seat
Sit On It!

Covers
Here's a look at the original 76 Grand Prix cover coming off, and the new 77 Trans Am cover going on. These are PUI reproductions, available anywhere. It's pretty obvious that the covers are the same. Side of the covers

Finished Seat Bottom
The reupholstered bottom is shown here next to the Grand Prix passenger seat. It looks pretty good compared to the Trans Am's poor original seats. I'm not very skilled at upholstery, so you should blame any wrinkles on me. Maybe it'll flatten a little in the heat of the summer!

Back Frames: Left vs. Right Differences
The left and right back frames are different because of the release latch, travel stop, and seat belt guide bracket. These are the Grand Prix Backs. You may notice that the shape looks like a standard or Chevy bucket seat. That's right, it's the same frame.
Even more shiny metal!
Note: This is the only piece of the seat that differs left vs. right.
Backs

Grand Prix vs. Trans Am differences
The 76 Grand Prix and 77 Trans Am have different seat back latches and travel stops. The latches (top) are not exactly the same shape, but they work exactly the same way. The Grand Prix (top left) has a rubber cover on the handle.
The travel stops (bottom) are even more different. The Grand prix (bottom right) has a slotted lever that slides on the striker bolt (not shown). The bolt is bushed with nylon. Very, very classy. The Trans Am (bottom left) has a little piece of cable that's flexed 10,000 times and wants to retire. Very very not classy. I believe this was used because the lever used on the Grand Prix hits the seat belt on the Trans Am when you slide the seat.
These mechanisms are welded on, so you can't easily swap them to another frame. This frame isn't trouble prone, and they made millions, so that shouldn't be a problem.

Swapping Left and Right Components
Ideally, you could build two seats using all passenger side components except the seat back frame. I decided to go ahead and try swapping a back foam bun onto the opposite side frame. The seat back bun, part number 9674248, was used on A, F, G, and X bodies and is the same for left and right.
Although the buns are interchangeable, during the last 25 years they have acquired left and right handedness, because the seat belt guide bracket makes a squashed place in the bun. Swapping the back bun creates a void on the inboard side, and makes the bun squash again on the outboard side. Here's how the bracket looked after it was all over. I wasn't totally satisfied with it, and I am going to trim the foam around it a little on the next seat.

It's all over
Here it is, softening itself in the afternoon sun: It's actually a passenger seat made from a Grand Prix driver's seat and Trans Am deluxe upholstery. I saved all the good parts for the driver's seat.
So, if you are restoring a Trans Am and having trouble with seat parts, rememer that you can make a spare passenger's seat into a driver's seat. A, G, and X body cars can be useful donors if they have the same type of upholstery. If you have a Grand Prix, you should be able to use deluxe Trans Am upholstery kits to reupholster your Grand Prix front seats. Unfortunately they are only available in vinyl.

Here's how my car looks with the seats installed. My favorite thing about this color combination is how the light gold of the hood bird complements the buckskin interior, while the dark color matches the grilles and wheels.

Side By Side Comparison Grand Prix on the left, Trans Am on the right. That's not the original Trans Am upholstery, but that is original Buckskin Perf on the left. The difference in condition of frames and buns is pretty evident. Two things to note: The grand prix seat is jacked up by its tall tracks The original trim panel can be seen at the bottom left, still in place. This height difference, purely accomplished by tracks, seems to have given people the idea that the seats are different. This prevented the Trans Am seat covers from being sold as Grand Prix seat covers up to now.
Seat Frame Here's the Grand Prix Seat Frame. It is still shiny after 25 years. Wow! My Trans Am seat frame is ashamed to get in the picture for comparison. That light stuff you see is actual shiny metal! None of the wires are broken! Eat your heart out. This frame is interchangeable for left and right seats.
Seat Bun This is the Grand Prix Seat Bun. It's in great shape. The part number is 9875139. According to the parts catalog it was used in A, G, X, and F bodies with custom interior. This is the driver's side cushion, but left and right are interchangeable. If you can't find a good driver's seat, you can start with two passenger seats and build one of them into a driver's seat. You'll note that this seat bun is designed for a "horsecollar". It was not changed from the 1973 upholstery. That means that all 73-77 Grand Prix seat buns would interchange. You can tell from the stripes that it was a 76-77 seat
Covers Here's a look at the original 76 Grand Prix cover coming off, and the new 77 Trans Am cover going on. These are PUI reproductions, available anywhere. It's pretty obvious that the covers are the same.
Finished Seat Bottom The reupholstered bottom is shown here next to the Grand Prix passenger seat. It looks pretty good compared to the Trans Am's poor original seats. I'm not very skilled at upholstery, so you should blame any wrinkles on me. Maybe it'll flatten a little in the heat of the summer!
Back Frames: Left vs. Right Differences The left and right back frames are different because of the release latch, travel stop, and seat belt guide bracket. These are the Grand Prix Backs. You may notice that the shape looks like a standard or Chevy bucket seat. That's right, it's the same frame. Even more shiny metal! Note: This is the only piece of the seat that differs left vs. right.
Grand Prix vs. Trans Am differences The 76 Grand Prix and 77 Trans Am have different seat back latches and travel stops. The latches (top) are not exactly the same shape, but they work exactly the same way. The Grand Prix (top left) has a rubber cover on the handle. The travel stops (bottom) are even more different. The Grand prix (bottom right) has a slotted lever that slides on the striker bolt (not shown). The bolt is bushed with nylon. Very, very classy. The Trans Am (bottom left) has a little piece of cable that's flexed 10,000 times and wants to retire. Very very not classy. I believe this was used because the lever used on the Grand Prix hits the seat belt on the Trans Am when you slide the seat. These mechanisms are welded on, so you can't easily swap them to another frame. This frame isn't trouble prone, and they made millions, so that shouldn't be a problem.
Swapping Left and Right Components Ideally, you could build two seats using all passenger side components except the seat back frame. I decided to go ahead and try swapping a back foam bun onto the opposite side frame. The seat back bun, part number 9674248, was used on A, F, G, and X bodies and is the same for left and right. Although the buns are interchangeable, during the last 25 years they have acquired left and right handedness, because the seat belt guide bracket makes a squashed place in the bun. Swapping the back bun creates a void on the inboard side, and makes the bun squash again on the outboard side. Here's how the bracket looked after it was all over. I wasn't totally satisfied with it, and I am going to trim the foam around it a little on the next seat.
It's all over Here it is, softening itself in the afternoon sun: It's actually a passenger seat made from a Grand Prix driver's seat and Trans Am deluxe upholstery. I saved all the good parts for the driver's seat. So, if you are restoring a Trans Am and having trouble with seat parts, rememer that you can make a spare passenger's seat into a driver's seat. A, G, and X body cars can be useful donors if they have the same type of upholstery. If you have a Grand Prix, you should be able to use deluxe Trans Am upholstery kits to reupholster your Grand Prix front seats. Unfortunately they are only available in vinyl.
Here's how my car looks with the seats installed. My favorite thing about this color combination is how the light gold of the hood bird complements the buckskin interior, while the dark color matches the grilles and wheels.