there are too many variances and variables at play, just from poor tolerances inherent to mass production ( with 60's tooling?) and possible repairs done in the past like milling the deck or head etc....or head came from a different engine.. there are head gaskets with different thicknesses, crush ratios... and maybe biggest of all, worn or aftermarket cams with unknown values for LSA, timing and duration. I have built a "few" engines, I don't guess, or take anyone's word for anything. I measure everything so nothing will bite me back later. Still often takes longer to "figure it out" than to actually build it. Seems like there are a lot of (*ahhem*american*cough cough*) builders out there that just drop parts into an engine and make it bigger, and they are happy because it (feels like it) is making more power. At least more noise.
Then they proudly preach how its the best way to do it.
