Yes, you can use a B-body 8 3/4 in a Duster if you move the perches. Flexing the springs that much is just flat out stupid, not to mention it reduces your tire clearance. If the wheel mounting surface to wheel mounting surface (or drum to drum) measurement is 59 1/2” then you’ve got a 65-67 B-body 8 3/4. I actually use a 68-70 B-body 8 3/4 in my Duster, it’s 60-1/8”.
But it depends on what wheels you want to run. You have to increase the backspace in order to run anything with much width. Before I went to 18x10’s with a 7” backspace I ran a set of cop wheels, 15x7 with a 4.25” backspace. With 225/60/15’s I was pretty much right on the quarter lips, no extra clearance to the outside.
With a 65-67 rear you’d have another 5/16” to the outside, but that’s it. Running 15’s with off the shelf backspacing you’d be pretty limited for tire width. If you want to run 17’s or 18’s it’s actually a great modification, because it evens up the backspace needed with the front.
