10 " wide wheel

Okay, since '73 Dusters never came with an 8 3/4 (factory switched to 8 1/4 in '73), we now know it was swapped in- but from what? An earlier A body? If so, do we assume it has aftermarket big bolt pattern axles, and the required big bolt brakes? Or are we dealing with redrilled sbp axles and drums? Or have you done the usual rear end swap from a B body? Have the springs been moved in, or do they remain in the stock location?
Sorry to sound so picky, but every thing mentioned will affect the size wheel you can use and what offset is required- and with a 10" rim there's no room for error, if it fits at all (and I seriously doubt it). Even the rear springs being used, and the ride height will affect it; as will the particular tire size used on that rim, since the sidewall bulge is where the interference is likely to occur.
In all honesty, I don't think you'll be able to fit anything over a 275 on an 8" rim into a stock Duster wheel well... That's about the max I've read that will fit, and that's with all the stars aligning on the factory build tolerances- but I've never personally pushed it that far. Most stock rear end setups don't like more than 4.25 backspace and 10" of rim width is going to require some sort of mods to the wheel well/tub/suspension.