[TKCR]

Just happened to be tearing down a couple of seat cores, and wanted to show you the difference in the foam.
This is the seat back foam. The one in the back is the 73-80. It’s is 2” taller, and almost 3” wider. Trying to show the width close up in the 2nd pic.
And then the next picture is the seat bottom frames for the 81-87, top. The 77-80 is the bottom. Again, the 73-80 seats are larger.
Pic #4 is the 81-87 seat bottom foam. Notice the holes along the back, those are for the seatbelts. The 73-80 foam does not have these.
Last pic is the ends springs that are always broken on the 73-80 frames.