One thing that might not be apparent, at first, is that most of the modern buckets are a bit narrower than the ones the cars used to come with. You sit "on" the seat, not "in" it, for example. Notice where your thighs are in relation to the edge of the seat. Another thing would be that the inside edges of the seat cushions are covered in a fabric so the leather/vinyl will not squeak against the center console as the seat moves up and back.
The other thing is the width of the seat's seat tracks in comparison to the width of the seat tracks on the intended "victim". Might need to make some 1/4" aluminum or steel plate adapters, as the dual exhaust R-cars had on their driver's side seats. Most of the aftermarket seat tracks are designed for a completely flat vehicle floor, which might not be the case in earlier vehicles.
Obviously, many late model seats could be possible to fit in the earlier cars. You might head out to a salvage yard with mainly late model vehicles, which should have some of those seats already pulled out and on a shelf for purchase. Take pictures and measure. I suspect that most will have lots of power adjustments, too.
Happy shopping!
CBODY67