Headers, cut the flanges or not??

I have an original set of Black Jack Alumacoat headers, have had them since 1982, when I built the stroker last year, the machine shop used a surface grinder and squared the flanges, I used mr gasket header gaskets, they leak, BIG TIME my engine sounds like a sewing machine, did some reading on this in here and bought Remflex gaskets, I dont want to do this again so should I cut the flanges or not?? the remflex guy said he's never heard of anyone doing that so he says his gaskets will seal WITHOUT cutting the flanges. so what do you guys think??