Personally, I would go with a small block rather than a big block any day of the week. Alot of people go with sb350 but I like sb400. I would build it myself, how I want it before I bought a crate motor. An old used chevy block isn't hard to find at all and it will probably be a tad cheaper depending on what exactly you're wanting to get out of the motor. And as stated above, might as well go ahead and build a stroker. For the few extra bucks, you get better HP. As for 4 bolt or 2 bolt, my dad and I have always went with 4 bolts. Always been pleased. Goodluck with whatever you decide to do.