I have a set of 339X heads. They have factory oversized runners of 170cc, but also have small intake valves, 1.72", for use in 307 engines. You might be able to get away with installing the 1.94" intake valve that is stock in all other heads and then you'll have some excellent flowing heads. They also have 74 cc chambers instead of 76 which may help bump your compression ratio the slightest bit. Installing the 1.94 valves might add that 2 cc's to the head, though.