The stock cam pretty weak any performance cam is a major improvement I'd go with a comp xe262h or similar cam from voodoo or whoever, from what I've read in the forums here the actually 318 chambers come out to about 68cc and 340-360 are about 72cc which if you mill them .020" should even them out with a thin gasket, I wouldn't mill the crap out of them just to gain a little CR.
P.S. if your thinking a 262 cam is too small it's a lot more cam than the stock 340 cam if you look at there .050" specs.
