Don, do the new distributors they sell now have the grooves all the way around? What was the original purpose for putting the grooves only partially around the housing? ThanksLook at the base of your dist./primer,there'll be a groove.If the groove goes all the way around,then it won't matter where the clocking is.If it's a partial groove,then you can either open it up all the way around,or when you put it in,locate the vac.advance mount in the approximate position that it would be positioned in on a normal engine.