will a 383 squeeze in a 73 duster?

If you've got the money, I'd suggest the Schumacher kit with mounts, headers and torque strap. Using it lets you keep the power steering if you want without having to modify the headers (with a hammer). Best part is, the Schumachers don't capture the starter. Mini starter is the way to go, too.

Does the car have A/C? If so, the blower motor may interfere with the passenger side valve cover, too. Don't forget suspension, brakes blah, blah blah, the list goes on. Schumacher's site, engine-swaps.com has a pretty good list, all in one place, of the things you'll have to think about.

Lotsa work, and a couple of buck and plenty of cursing, but once it's in, it's worth it!