Magnum Head Qs

Yea Adam, I'm sure. I did the same thing myself. The magnum head has a small port on the exhaust, the same as a 318 port, and the hipo 340 exhaust manifold is a tall port to match the 340 head.
I made steel plates with a magnum hole size and a 340 manifold outside diameter.
Don't feel bad, many people don't know this. I contacted Hughe's engines and they said they never herd of it either.