'71 Duster 440 or 360? Pros and cons

Don't swap to the 440 till you've been able to make it worthwhile. As it is now, it's probably an 8.2:1 comp motor, and won't run all that great unless you cut the heads and do a lot of tweaking.

Start buying good pieces for the engine and drive line rebuild, find a good shop that knows Mopar, and start getting the chassis ready to handle the swap...all while you drive it with the 360.

and don't go crazy with the engine build - you can go pretty damn quick with a mild 440. The car in my avatar had a 9:1 standard bore 440, .474 hyd cam, msd 6al, Holley street dominator intake, stock 4779 Holley, 2" CPPA headers, stock hi-stall converter, 3.91 sg rear. Best it ran was (corrected for sea level) 11.69 @ 116.86 on pump 92 octane. Not my quickest car, but was actually the most fun, because I could drive that thing anywhere, anytime (and I did).