These measured 56 before being ported. I THINK that's about what the stock production heads are, I'm not sure. I haven't measured any of those yet. The only other one I've measured is the one on Vixen now that was milled heavily and it's 34CCs.
the slant heads combustion chambers that I have cc'd are all in the 57-58 range, those have all been the newer peanut heads. One cc could be in the choice of sparkplugs, filling technique.