My 2020 rulebook clearly states:
"Phenolic spacer must be flat across entire gasket mating surface, with a minimum thickness on gasket surface of .265" (not including gasket). Gasket surfaces must remain parallel ... no angle cutting allowed. Center inlet hole is NON-TECH (size, configuration, finish), but no rifling, grooving, dimpling, etc. allowed. Maximum mounting holes(s) size .300" NO-GO (checked with .300"+ pin gauge)" Phenolic spacer/gasket(s) subject to spray test to check for leakage or introduction of air into intake track.[sic] When performing the spray test the engine may stall or speed up, both indicate that the engine has failed this test.) Length of carburetor mounting stud I[sic] non tech. (Gasket Matching Allowed)"
Is it a new rule that it must be D shaped? Please explain further.
EDIT: I'll tell you right now, mine has been gasket matched to the carb and intake port. It may not make any more power but it makes me feel better. It is still D shaped but certainly ported.