1975 Charger Drivetrain Into A 1973 Duster?

Whew, thats a tall order you're facing!! First off, the 9 1/4 from a 71 and later B body is the widest unit you can find except maybe the C body units, way too wide to fit under your car, even with offset rims. Narrowing it will cost much more than finding an 8 1/4 A body unit and rebuilding it with a SG unit and all. I'd try to go the 8 1/4 route if you can!!

The motor would bolt in with some Schumacher mounts but the trans may hit the tunnel, being a bigblock and all, but nothing you couldn't overcome!!

JMO, but I would consider a nice potent smallblock coupled with an 8 1/4" SG rear, it would certainly make life easier and be lighter in weight than the B/RB motor!! Good luck with whatever you decide to do!! Geof