[War eagle]

Strange thing happened while rebuilding a 64 center carb (orig) and trying to fit an aftermarket power piston. The washer that pockets into the air horn is large compared to the one removed. The original measures .402 while the aftermarket is .410. Even if someone has "staked" the original and closed up the pocket, it would never have accepted this .010 over washer when new. I opened up another known tripower carb and it too has the .402 diameter washer. I save everything and in the last 40 years have even kept used power pistons from 283 chevs to everything else Rochester and I don`t seem to have that large washer on any pistons. Any ideas out there carb Guru`s?