Brett's right about the cam - a little goes a long way in a 350. Also consider finding some 1967 - 1970 large valve 400 heads. (#12, #13, #16, #48, #62 or #670) The 72 cc chambers will be almost perfect for a 350 build. Use a stock intake and Q-jet, and either the 068 or the 067 cam and you'll have a killer combination - basically a pump-gas version of the 350 HO. Headers or Long-Branch manifolds would top off the project nicely.
I know you're on a budget and you want to use as much as you already have, but if you want to really step up the performance, you might want to consider some upgrades.
