'interior interchangeability

Do 66 / 67 A body bench and buckets interchange with 68 / 69? Looks like
only the upholstery patterns differ.
Tx guys

No, 66-67 A-Body bucket seats have hard back and no catch so the seat backs don't go forward. Bench seats differ with the catches only.

Tx SS..how would you access the back seat on a 2 door '66 dart with buckets?
...do they just flop forward when required?

I believe these are '66 dart and as you say i don't see any catch or locks for the backs.
...will they match with front '68 mount holes and will the rear bench fit the 68 rear brackets?

1st generation bucket seat tracks are quite different form 2nd gen', wont work. We can't see what tracks are under those buckets but the hard backs do have the carpeted toe kick area so 66 is probably correct. Pretty much the same seat frame, except the upper member of the bucket back frame is tubular. In 67 up that member was formed to square and has provisions for head rests. The earlier tubular member makes the back frame a good 1/2 inch taller than the 67 up. Later covers do fit but not exactly right. Binding hem at upper corners peeks out from under the hard back. I'm pretty sure 1st gen' rear bench would be different from 2nd gen too, narrower, back a little bit shorter.

Tx RF!