Check out Langdons stovebolt page at
www.stoveboltengineco.com They have pictures and prices in their online catalog. Just for bolt on HP you could get a set of headers, a 4 bbl intake and carb, an HEI ignition and throw on a K&N filter kit. That will give it some more boost.
I was in the same boat as you, trying to decide on the built up inline or a nive 350. The 350 won by a landslide and mainly because of 2 things, the cost of the rebuild, and the performance. It is costing me in total about $1000 to rebuild my 350, that includes the $350 I paid for the engine . Where as the inline was going to cost me 3 times that amount. PLus the 350 has more parts readily available for performance upgrades. But as others have said. I would love to have a screamin six someday. Good luck bud