magnum head cam?

cc'm still but 302 heads have the same if not a lil bigger chamber than the stock open chamber 318 heads.

ME?
I would maybe advance the cam a lil or degree it in to begin with if not already, run the 600 holley vac sec, and play with the timing curve and fiddle the carb to run best with the 318 heads on it OR cc/mill the magnum heads to get the same or more compression than you have with the 318 heads.