I finally confronted the problem that my old machinist made for me by gasket matching the exhaust ports on my vortec heads. I realized that the headers I have been running are seriously restricting flow since the primary tube is 1.5" and even smaller at the flange as opposed to the much larger ports. I looked into larger headers for the 4.3l v6 and found there are no options for a larger primary tube unless custom made. Hooker Super Comp used to make a pair but discontinued them. So now the only option I have is to go back to stock manifolds. Supposedly these manifolds are not very restrictive until you go over 300hp and I am going to run a cutout after the crossover pipe. Is there a significant advantage in having them ported? The port size is (i think) exactly the size of the flange on the manifold and I would like to have them opened up a little to prevent reversion and maybe have them polished to improve flow. This will be done by a different, more reputable machine shop by the way if I get positive feedback on this.