Correct the heads are the same no matter what the bolt pattern.

Clearance was the main reason they used a diagonal pattern. There was not enough room to install the lower bolts in the 390 Mustangs, Cougars, Comets and Fairlanes. So a new exhaust manifold was used with the diagonal pattern. This allowed the clearance needed between the head and manifold. The exhaust manifolds and heads were the same for the 390 GT or std 390 when used in the cars listed above. I might have missed one or two models. Over the years the heads and manifolds have been "nicknamed" GT heads even tho they were used in non GT versions.


G.