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Somatic Negative Optimist
Join Date: Mar 2002
Location: Winlaw, BC, Canada
Posts: 7,206
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If they are '78 SC-heads, they have a groove machined into the top of the cylinder to receive the Alu crush seal. Do you have the grooves? Have these heads been machined in the spigot where they mate with the cylinders?
(3.2 Carrera engines don't have these grooves)
As I see it, the diameter is not so important.
What is important is the equal height of the cylinders, and the equal height of the heads so that when you mate the cam tower to the heads, no height difference in the cylinders/heads results in leaks.
Are your cylinders of the same tolerance group?
Have the heads been machined to the same, equal height?
The cylinders, and heads, from one bank (1,2,3 or 4,5,6) have to have the same height.
A competent machine shop will know these issues and can check the measurements for equal height.
When heads get a valve job, this spigot where the cylinders mate with the heads, get a slight, equal shave, just a few thou unless there is damage there and more has to be taken off (Equally on all 3 of one bank)
It sounds to me that you need a competent shop to check these issues.
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1980 Carrerarized SC with SS 3.2, LSD & Extras. SOLD!
1995 seafoam-green 993 C2, LSD, Sport seats. 
Abstract Darwin Ipso Facto: "Life is evolutionary random and has no meaning as evidenced by 7 Billion paranoid talking monkeys with super-inflated egos and matching vanity worshipping illusionary Gods and Saviors ". 
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