Original Rear end type on my 70 Duster

I've seen this:
View attachment 1715923710
So given the previous replies and this chart, a 7 1/4 OR 8 3/4 COULD have been in the car.

Yes. Although in ‘70 I think a V8 would probably have gotten an 8 3/4. I don’t remember the exact year break, a 318/auto could have come with a 7 1/4 for some years but I think that stopped at some point.

But as far as I know an 8 1/4 with SBP was never available, so they wouldn’t have been in A bodies until ‘73 when the V8 cars went to BBP disks. I know the B-bodies came with them earlier than the A’s, I have a ‘71 Satellite that has a 383/727 and an 8 1/4.