250 Exhaust parts?

[Joe Z]

I have an 81' c10 with a 66' or 67' inline 6 250 in it. I just got it back together and running but now I can't find a (I believe doughnut gasket? This is what the guy at the parts store said) for the down pipe. I've tried online and at a few auto parts stores and everywhere I look it's discontinued or out of stock indefinitely. I never had the stock pipe for this motor but it appeares to not have a standard flang and requires an oblong steel ring with two bolt holes and a rubber center ring? Can anyone help? Not quite sure where to get the part but the part number the seems to be coming up is 31851 at autozone as a walker part. On rockauto a steel ring comes up but no mounting equipment so I'm not sure what the right part is or how it's supposed to go together. Any help would be appreciated, thanks.