The cheap and "bush league" way of grinding the flanges on my headers have seemed to work out just fine. I'm not an expert mechanic, but the guy who showed me the way is. I have about 2k miles on the truck since and everything works great. As NM51 said, the flanges are of different thickness on these new fentons and so a mill would not work. As far as not creating unequal pressure - the key is to grind little by little so that it doesn't get overdone. That's why the bench helps so much. I took each header on and off about 20 times to make sure it was just right. The hold down bolts are level and parallel to the block. The fit is good. But don't let me stop you from going out and spending your money to have some else do the work for you. If I had to do it again, I would be patient and find a set of original fentons that actually fit. For the 261 that I'm building, I'm going to do that or I'm going to split the orinal exhaust manifold. Still riding the fence.
