The 164 shop manual that I have, it is a copy with no title page, gives the allowable thickness of the cylinder head with a range from 4.91x inches from the base of the head to the center of the cam. Measuring my front head, I get a much larger dimension. Is this the right number? What I am after is how much to mill a stock head to end up with a 10.3 or 4 compression ratio, but I can't tell if my head has already been milled or not. I did search for threads but couldn't find this.