Josh, welcome to the stovebolt page. Sounds like you have a 3/4 ton frame - going with 6 lug (1/2 ton) running gear would be much easier if you had a 1/2 ton parts truck to swap front and rear axels - although I have no idea if the spring perch locations are the same width between 1/2 ton and 3/4 ton.
I know a lot of rodders prefer the 3/4 ton frames to build. As far as 6's go, if you want a vintage hot rod look, go for the GMC 302 or chev 261 inline 6. If you don't care really about a vintage look drop a 292 6 in it with a modern bell housing and easier choice of trannys. Lots of choices on which way to go. For a lot of inline 6 information go to
http://www.inliners.org
