I'd add a #5 to Bill's list
5) How do you feel about Maintenece (mechanical/body/etc)?
If can do alot of the work yourself then perhaps changing engine parts, suspension/wheels/etc over time from someone else's build is not a big deal.
But if you are looking mostly for a 'get-in-and-drive' car without having to fiddle, then I would say focus highly on the build quality of the car you are looking at.
Big block/small block/etc - either one you wind up with, you'll have a car that very very few people have and some actually never heard of! any everyone will love it
So if you are mechanically inclined and tracking down issues isn't a big deal, then you probably have a much wider variety of car to choose from.
I assembled my replica myself and its been 98% done for a year now
I think in 100 years, it will 99% done....always some to play with or try a little different. but it is hands down the best car to drive anywhere.
good luck in looking!