another option, vs. buying used heads, or putting bigger (new) valves in are to pick these up from hughes:
Enginequest 318B "Iron Ram" heads

they basically flow OOTB better than a max ported 318 head with 2.02/1.6" valves will flow, are new, and have a nice spring package on them. you can find magnum rockers used for about $30-40 from the junkyard or fleabay, or about $90 new from rockauto, just get some 7.625" or so pushrods, and you're good to go. for a driver cam, I'd look at a lunati voodoo 60400 or 60401, or a comp XE250 or XE256