You need to figure out what kind of flow your heads have,
http://users.erols.com/srweiss/tablehdc.htm#Chevy. You can make up for lack of flow with a big cam but you really have to be spot on doing this. The cheapest way to get power is to stroke it, which depending on how how much work your block and crank need might end up cheaper. Also, if the heads are really crappy or need lots of work it is way cheaper to buy better ones, ebay has some great deals if you look around. I don't know your budget but the comp cams website has lots of cheap build ups in the articles section.