'71 Duster 440 or 360? Pros and cons

In my humble opinion you should go with the small block. The money you would spend on headers, engine mounts, k-member mod's, a 727 trans/torque converter, driveshaft modifications, big block radiator/hoses, fan shroud, bigger battery, torsion bar upgrade, and the time you'll have chasing down the correct parts just wont payoff in the end, unless you just want the bragging rights that go with having an A Body with a big block. Hey, there was a reason for Dodge/Chrysler/Plymouth to put a B/RB Engine into an A Body but they had an unlimited budget.
That said, I'm not far away from finishing my '67 Dart GT with a 383/727 which was originally a 273 car. I love the sound of a Big Block Engine. I have 235/60/14's on the rear with a 3.55:1 Sure Grip, Traction Bars/Pinion Snubber that I'll just dig wicking it up and smokin' the tires as far as I want to.
The moral of the story: Its the swap from a LA to B/RB that makes it expensive. If your on a budget stick with the small block, it will definitely put a smile on your face at a much cheaper price.