Should flange thickness even matter, though? As I understand it, the primary tubes extend through the flange, so in theory the flange itself does not determine how far off the exhaust ports the header ultimately sits. I'm guessing it has more (i.e., everything) to do with the larger 1-7/8" primary tubes you have with the D567 units versus the 1-3/4" primaries on the D564s.
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1966 Pontiac GTO ( restoration thread)
1998 BMW 328is ( track rat)
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