I have a Fenton dual carburetor intake and the Fenton dual exhaust manifolds. No grinding was necessary to use these together. They are made to work together.

When I bought an Offenhauser dual carb intake and a Fenton dual exhaust manifold from Patrick's about 15 years ago, I had to grind the "ears" on the Fentons and grind a little aluminum off the Offenhauser. Patrick's provided an "instruction sheet" that only stated that Mr. Fenton and Mr. did not confer with each other, and a little grinding would be necessary to get these manifolds to work together.

I'll find out soon how much I'll have to grind my Fentons to get them to work with a GM original intake manifold (I'll be using a two-barrel Holley AA1 two-barrel carburetor with variable jets).

My guess is that those Chinese-made Fenton headers are made to specifications.