Only the 67 models had a folding seat option. Some 68s might have gotten them, too, but federal safety regulations took it away sometime in 68.
On the later seats some people will leave out one of the screws holding the seat back to the seat bottom to make it fold, but you have to re-engineer the upholstery to make it work. You will see what I mean if you really study how the upholstery is done.
I think there are basically three different versions of these seats.
1) Early Version 67-68 +/- had coil spring bottom with thin foam, 2" +/-, and from what I have seen, foam backs.
2)69-70 had flat spring bottom with thin foam and foam back.
3)71-72 had full foam bottom and foam back.
I had purchased a middle version for my truck and did a whole restoration and new cover. There are some pics on this thread.
http://67-72chevytrucks.com/vboard/s...d.php?t=735220
I found the seat looked good, but did not ride well.
Then I found a 71-72 full foam bottom seat and did a full restore on that one, and swapped out the cover. It looks great and rides really well.
You may not need new foam. I decided to just repair the foam I had. the driver's side bottom and back foam needed repair. You can see some of my foam repair in the thread referenced above. It is pretty easy to do. Just go on youtube and search for automotive seat repair. You will find a bunch of videos.
I did all of the work to the two seats, and as I have said before, I now know why upholstery shops get the money they do....you can really work up a sweat!
Here is a pic of my grand daughter enjoying the refurbished seat.
Good luck, and if you have any questions feel free to PM me.