do you have the seat belt running through the head rest bracket ? my seat bounced around until i put those brackets back on after haveing the seat done. i think the seat stop is part of the pivot on each side. should be a flat tab that sticks out and the seat back arm rests on it.it should have a rubber pad on it.the early cars used a bumper screwed to the seat base
I adjusted the tilt of my seat by using a spacer under the rear seat legs. I prototyped it with large nuts to get the right thickness and then used aluminum blocks and longer bolts. Half inch blocks was all I needed.- in the end for my seat.
I'm not sure about the benches but the upgraded buckets in mine (Monte SS seats) have no adjustment and only the inertia thing to keep them from coming forward suddenly. I have read some things here about placing wedges between the bottom and back to make it sit more upright.
The site "grandaman" shows a new seat back stop repair bushing (in the picture) and is from a ford tailgate bushing. NAPA p/n 675-5144.
I don't know if it's for buckets, bench, or both. Go and take a look.
Oh, the Grand Am is is the same as a 5th gen. so it should work on your '86.
On my 5th gen, the outside hinge sets the angle of the seat back, at least on my bench seat. The seat back portion of the hinge bears against the the back of the lower portion of the hinge and uses it as a stop.
While looking around for something I could use as a spacer, I measured the width of the hinge slot that the seat back bracket moves in, found a nut the width of the slot, cut a slot through the side of the nut, and slipped it over the back of the slot so the seat back bracket bears against a side of the nut using it as a spacer moving the seat back forward. It seems to work well and has stayed in place. If you could form a piece of metal that would stay in place, that fits over the back of the hinge slot you could make it as thick as needed to set the angle to your desire.