Nothing wrong with the stock heads except they take a specific intake. #178, 234, and 920 heads are good ones. You're heads are probably #080's. As 65Val mentioned, the #302's are a good head for 273's as well. They have 273/318 sized ports, small closed chambers and a bonus of hardened valve seats for unleaded fuel. A wanted ad is a good place to find them but shipping is always a issue because of the weight.
