Went through this a week or so ago if you haven't solved your problem yet...
Helps with the seat out of the car, if you remove side trim around button (may have to pull plastic seat back off, or at least loosen it), you should have access to 3 bolts that hold the latching/release mechanism in place. If it is so frozen you cannot convince it to let go, you may have to creatively take out the screws that hold the striker in the seat bottom. CAREFULLY peel up the corner of the upper seat cover and you can wiggle the latching mechanism out, took me about 20 minutes to get mine out. At that point, you may find like mine it was dry and rusty, needed alot of WD40 to loosen it then alot of lubricant to keep it moving. I was probably 1 hour "round trip" but got mine functional again. If you have a donor seat, the actual latch is the same I believe from 71-74 although the trim and buttons are different. Nothing you can see or do from back seat anyway, so size shouldn't make a difference.

Just a pain trying to convince an almost 40 year old part to cooperate.
