In 1983 the base gasket for the new Evolution cylinders was assigned the part# 16777-83, which was almost immediately replaced by 16777-83A. In 1986 the part# 16774-86 replaced the older 16777-83A gaskets and the part# 16777-83(A) disappeared from Harley litterature. The outline of the 16774-86 gasket underwent several changes during its span of use. But despite of the different outlines any of these gaskets fits a stock Evolution engine from 883 to 1340 cc.