What's a good rear end to put in my Duster?

A '60's B-body 8.75 is easiest/cheapest way to go. No need to move spring plates.
Use spacers(or even stack of washers)on rear shackles so each rear of spring is
Spaced an inch or so outward- that's it! Dusters have open wheel openings so
tire clearance isn't a prob. Did you ever notice on a disc brake Duster front tire track
is wider than rear? FIXED! 4.5" bolt pattern, bigger brakes, very simple and cheap.
Me and my brother both did this on our Dusters.