12 bolt shoppers beware !!!!!!

[Jim Ferron]

OK Here's the answer...Pontiacs had two styles of valves covers...the 389 style, '66 and older, you know the ones, they didn't have squared shoulders, they fit 326-389-421...and 67 and newer style that fit 350-400-428-455.

They both had the same bolt pattern but the 66 and older sat about an 1/8 lower on the head.

If you put a 389 valve cover on a 455 engine the rockers just hit in the sections of the valve covers that aren't 'squared' off. An extra set of gasket cures that ill. So plenty of 65 and 66 GTO's have 455 engines in 'em and you'd never know except look for two sets of valve cover gaskets...[or now I guess everbody just memorizes the casting numbers]