moog "hit the nail on the head" as we say across the pond.
If your case was just opened up for larger p/c's then its could be the piston tops are a little thicker on top than one another(quite common), but if the case was "bored and decked" then one of the decks could have been machined a little too much
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P.S. you have a e-mail w/autocad program
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1970 T1 W/MassIVe 2913cc RAT/?EFI? w/direct fire (very soon) and 915 trans
1962 SC 1776cc SP 944NA brakes, 993 wheels
VKG