I have used a mock up head to set things up and it is the greatest help of all. Even better is to use the whole engine, if your engine is on an engine stand.
To me the best of all worlds is to mill the header flanges to the same thickness as the flanges on the intake you are using. By doing this, the flanges are both on the same plane for the clamps to work correctly and apply the even pressure needed to seal the gaskets, the headers should fit correctly and the unit should be close to in line for your linkage to work correctly. If the headers didn't fit correctly, my next choice would be to grind on the headers where they pass under the intake. I think it's worth the price to have the header flanges milled to the proper thickness. Finally, let me say that if you can find a vintage set of Fenton headers, even though the price might be higher, that is the best way to go. The extra in a higher price will pay for itself.
Joe
