'71 Duster 440 or 360? Pros and cons

That is the later pump housing. They changed at some point in the early-mid 70s. No big deal. You can run it or get an earlier housing (there are a couple of different ones of those, too). Alternator brackets are particular to each one.

For me, I'd go with the 440, but you will need to open your wallet a bit. It's not that hard a swap, but make a plan before you jump in. Spend some time wandering around the tech pages at www.bigblockdart.com to help make the decision.