302 heads...were to buy..what works with..?

There are 350 hp 318 combo's out there with stock heads, but not stock LA 318 heads. Your best bet for 350hp with "stock" heads would be to use the later 5.2/5.9 magnum heads. There are several magazine builds using magnum heads that managed to get 400 hp out of them without modification.

The 302's have small 318 style ports, so while they're good for velocity they don't flow flow as much. Plus, if you don't have a set of 302's already, you can buy a set of new or rebuilt magnum heads for less than it will cost you to buy and rebuild a set of 302's.

Only things to keep in mind with the magnum heads are that you'll have to use a magnum style intake, run the magnum pedestal rockers (which are 1.6 ratio rockers), and make sure you have oil through pushrods and lifters. But, if you make those changes, you'll end up with 1.92/1.62 valves, much better flow, and closed chamber heads that are usually around 60cc's for chamber volume. That will get you pretty decent compression numbers using flat top pistons, even without zero decking the block.

Here's one of the 400 hp 318 articles, this one uses magnum heads...

http://www.moparmusclemagazine.com/techarticles/mopp_0409_318_engine_build/index.html

Here's another, this one using 302's. You'll see that to get to 400 hp they had to do some porting on the 302's, plus larger valves etc. After you do all that, the magnum heads would be far cheaper.

http://www.hotrod.com/howto/113_0304_318_small_block_build/