Slant 6 exhaust leak.

The flange is the same as either side of the big block. The gaskets I have, have a 2-1/4 hole, same as the B B flanges.
I gasket matched the manifold outlet to the gasket I have.
The manifold flange hole as cast in mine was 1-7/8 diameter to start out with. And well off center. In order for the hole in said gasket to line up with hole in manifold I had to grind heavy on one side, and didn't touch about 1/4 of the hole.