Anyone look at an XJ cherokee rear end for a BBP conversion?

If they're 59.5" drum-drum then they'd basically be the same as a 65-67 B-body 8 3/4 for width, which is very doable for a Duster but your rim/tire goals will be important.

You'd need a conversion joint for the yoke and you'd need to have new perches welded on. The driveshaft length change would depend on what you've got in there now for a rear axle, I'm assuming it's a 7.25 otherwise we probably wouldn't be having this conversation.

The 8.25 should hold up great behind a /6 or mild V8, they're not quite as strong as an 8 3/4 but if you're not making big power or doing any significant drag racing it shouldn't be an issue as long as the 8.25 is in good shape.

The wheels you want to run are definitely a consideration, if you're looking at 15" wheels and want to run wide tires out back the wider rear can be a disadvantage, you need to run more backspace. I have a 68-70 B rear in my Duster, it's 60 1/8" drum to drum and with a stock 15x7" with a 4.25" backspace a 225/60/15 is the best you can fit in the wheel well. You'd have a little more room, but probably not enough to get a 235 in there on a stock 15x7. If you wanted to maximize your tire size and are going to keep the leaf springs in the stock location you'd be looking at a 15x8" with around 5.25"- 5.5" of backspace, which will put you into custom wheel territory. Of course you're welding on new perches, so, if there was ever a time to install a 1/2" spring offset now would be the time. But that just makes the backspace issue worse, since it basically means adding another 1/2" of backspace to take advantage of it.

Now, if you're looking for 17" or 18" wheels and want to maximize your tire size a 9" wheel with around 6" of backspace would do it with stock leaf spring locations and that 59.5" wide rear, and that's a fairly easy to find off the shelf wheel. So that wider rear axle is no problem if the plan is 17/18" wheels. If the plan is to stick with 15's, well, it very well might mean a custom offset wheel if you want to run any kind of wide tire back there.

Those are all just rough numbers for the backspace, you should measure your own car because they're definitely all a little different and if you really want to maximize your tire size the factory tolerances make a difference. I'm just basing those numbers on the measurements from my cars, and using the 59.5" dimension for the rear axle.