Mitch---OK, the head is "newer" than you thought and not from a '73. To
get the 9.5 compression ratio you're after the final head thickness
after milling will STILL be 3.425. Only the amount needed to get here
will change from the previous information, so let's plug in the formula
that's based on knowing the ORIGINAL compression ratio.
8.5 (-) 6.5 divided by 8.5 X 6.5 X 3.74 =
2 divided by 55.25 X 3.74 = .135
The amount to be milled to get to 3.425 should be .135 based again on
what you reported the head thickness being 3.562.
The .020 over on your bore doesn't do much in changing the C.R. and
should be discounted. Only the stroke (3.74) is needed here.
You also mentioned...
The roller rockers @ 1.55: 1 and the $$ spent here is more personal
choice. If you have the bucks, do it. If you're watching the budget, do
it last, if at all. Same with springs, single or doubles being a
choice.
Hope this is clear to you and all interested in such things. Feel free
to question any or all of this.
Dick T.
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