Magnum Exhaust Port Dilema

Here is and old Hot Rod Magazine article by Steve Dulcich. Do not alter the port shape. Make a set of exhaust manifold gaskets. Not hard to do. It is a common practice on the LA style heads to weld up some of the exhaust ports of headers and grind the header to match the port. TTI can do this when you order direct from them and tell them your application.
Magnum R/T Cylinder Heads - Mopar Muscle Magazine