When I pulled the stock box from my 56 and shims fell on the floor I posted a question on this on the other site and the mental giants over there said no way they were OEM. [RickL said he personally had not seen them on 55-57 but had on Chevy II] Yesterday I pulled the box off this rough old 57 I am worling on and what fall out a shim. I guess that I am the only one who finds these things.