273 needs new heads, suggestions

Thanks for all of the feed back everyone. I think I will try to do a leak down test this weekend to get a better idea of what is actually going on. I will also pull the engine/head numbers this weekend. Then if it points to replacing the heads I will look for a 273 replacement heads (or if I cant find good ones ill have a shop fix my stock heads). It is sounding like the 318 heads might also fit? Or are the valves on 318's too large to fit without modifications to the block?