'71 Duster 440 or 360? Pros and cons

Actually given what you just said, I would recommend even stronger that you do the big block. I don't know your age, but my wife and I bought a 68 GTS convertible in 1983 (I was 23 at the time) with a 340. Neat car and plenty fast enough in stock form, BUT I always wanted to build a big block a-body and that was the WRONG car to do it to (one of 271 340/auto 68 GTS convertibles sold in the US).

So, in 1988 I picked up a 67 Dart GT hardtop. I put a stock 350hp/440 in it with a four speed, 3.23SG 8-3/4 rear. I never finished the cosmetics because it was such a blast to drive (I also built the suspension to handle reasonably well). Then my older son turned 16 and needed a car to drive. That was his daily driver for a year and a half...The car is long gone, but he AND the parts survived to be put into my other son's 67 Dart GT convertible and now I'm building myself a 67 Barracuda convertible that will get a 440/auto.

I really doubt that the 360 will be enough different than your Nova (although being a Mopar WILL handle better) to feel like it was worth it.