Headers vs oem manifolds

I installed a new set of Thorley Tri-Ys on my 454 P-30 in April.. When they came they looked great, but I have habit of checking out all parts before installing.. When I put a straightedge on the header flange I found it was warped from the welding process about 1/8" to 3/16". Instead of sending them back to the left coast and waiting a couple more weeks, I took them to a neighborhood machine shop and we put them in the hydraulic press and pressed the flanges straight, and then used a large 30" horizontal belt sander to sand them perfectly flat.. There was minimal material removed, but the moral of the story is that if I had put those new headers on like that, They probably would have eventually leaked too.. The Thorleys really helped on performance and heat removal..