Show me your wheels/tires
Gonna be pretty close to the springs with a 4.5" backspace and 275/60/15's. The 8.25 is narrower than than an A-body 8 3/4, especially with BBP axles. The 8.25 is about 1" narrower overall, so about a 1/2" narrower per side. The 15x8, 4.5" backspace is typically what works with a 8 3/4 with BBP axles. Although honestly that combo usually ends up right at the edge of enough clearance to the outside.
You may find that you need a small spacer (<1/4") to get better spring clearance, although that's a better spot to be in than not having enough room to the quarter.
There's a bunch of threads about putting 275's on Dusters with pictures. Just remember that what works for a Duster/Demon with an A-body 8 3/4 and BBP axles may not be exactly what works best for you with the 8.25".
275/60/15 woes
275/60/15 tires on stock Duster
Duster 275/60/15