Im running remflex solid graphite gaskets with my 3"catback to 2.5" stock cat/ downpipe.
I dont know the part number but just do a google search. They are super thick and fill pitted and warped flanges. Also they rebound and do not require a retorque. Good up to 3000 degrees. Only 12.99 on ebay. I used the gaskets my catback came with and they leaked even torqued way beyond spec.