What is the diferance between a 55 and 56 chevy 235?? I have 2 55 blocks, 1 first series and 1 second series. Second series serial number by dist. is F255x. the first series number is F55mb.Sealed power lists a CS 293 mech. cam as a 261 cam, but it says it will fit 56 to 62 235. why won't it fit a 55 block??
