Best starting point for V8 swap

Looking for some sage advice. My 73 Duster with /6 just isn't doing it for me any more so I am looking at a V8 swap. I will be using the schumacher kit but I need to decide what engine to start with. The local wrecking yards have the following engines. 75 360 from a 300 series van, a 92 360 from a van, various 98 5.9 magnums. Also there are a few 318's from 98 back to 78.

Which engine would be the best place to start from taking into account availability of performance parts and upgrades (I want to stay carb'ed). In the end I want to be able to use pump gas 89 or 91 octane, get good mpg 18 to 20 (not sure if this is realistic) and a fairly easy swap with either a 904 or 727.

Thanks in advance
Brent