I have Kooks LT's w/ OEM gaskets that I got from the Chevy dealer. I'm assuming they ordered by VIN so they got to right ones. First, do LS1 and LS6 have different gaskets b/c the LS6 head has D shaped exhaust port? 2nd do the OEM gaskets restrict flow in any way w/ headers? I was told this but I don't believe it to be true.