help me build my first race car

IMO, if you are on a budget, go with a small block. It might cost a little more for the engine itself, but you need to take into account the other added costs of making the big block fit and work in the chassis. There are engine mounts out there that allow you to put a small block in a /6 K frame, but I don't think there's anything to go from/6 to big block without doing some fabrication. Plus, like everyone else said, you need to get the chassis set up first. When I built my Duster, I had the frame connectors, dana, race transmission, suspension rebuilt, etc while i was driving it around with the 318. Once I got the stroker in, all I had to do was some tweeks here and there.