Eric's right, you have to maintain the relationship between the friction surface that the pressure plate mounting surface. I swapped a tranny in and out of my HP Rabbit way more times than I should have had to because the p/o had an incorrectly cut flywheel.
If there's any irregularities (minor), I use a 'cookie tool' in a right-angle die grinder.
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MARRS #25 ITB Rabbit GTI (sold) | MARRS #25 HProd Rabbit
SCCA 279608