I think what Kerry posted is the smaller 2" Header-to-precat doughnuts, and you need the larger 3" doughnuts.....right? You may have to have someone "tweek" the flanges & pipes to get them parallel. Then get some new doughnuts, grind one side flat and leave the other side chamfered. Am I picturing this right? It may help if you post a picture? And if you can limit the amount of sealant used, I agree with the others that ultra-copper is good stuff.