http://www.inliners.org

http://stoveboltengineco.com/index.htm

http://www.cliffordperformance.net/index.html

Here are a couple of sites to check out.

The 302 GMC (Jimmy) was the hot straight six back in the fifties and sixties; parts for them are getting hard to come by, now. I knew a guy back in high school who regularly thumped many of the popular V8s of the day with a hot 302 Jimmy in a '51 or '52 Chevy; saw him run against a '58 Impala 348 Tri-Power and flat run away from it.

Today, the big Ford, and the 292 Chevy would be the ones to build, if you want size. Mopar slant sixes are good performers, too.