318 pefromance help
I keep hearing the 302 heads are the ones to use. Look for 318's made between '85-'91.
Another option is a set of 360 heads. They must be shaved for use on a 318 so that it doesn't kill your compression ratio though. You do gain bigger valves over the 318 heads.
Aerohead racing (google it) is a great way to go. You can get a set of 318 heads from them with heavier duty valve springs and larger valves. These are ready to bolt on for $399. That's hard to beat once you figure in the price of having a set redone at the machine shop.
I think the 340/360 heads are about $500 as well.