So if the factory pipe lasted for 20+ years, how long of a time would be acceptable,10 years? I'd have the muffler guy fab the piece you need.
This is what was done on 3 of my Jeeps, the shop made all the parts from the manifold back. If Longevity is a concern , have the pipe made and take it home and paint it with hi-heat header paint and follow the directions on the can.
My guess is the pipe will outlast a ordinary Aluminized muffler.
1957 WILLYS pickup, needs work.
1973 J 4000,
1978 CJ7 DD.
1979 CJ7 360, TH400/Quadratrac trail Jeep.
1980 CJ5 trail Jeep.
1983 CJ7 pretty weekend and sometimes to work Driver in the summer, My first rebuild, if the Q-trac and 5 are broke, this one is the one to take. its just as capable as the other 2, except nice paint.
1984 Grand Wagoneer, 1 ton axles, great 360/727, and a big a$& tree fell on it .
1989 YJ the CJ to YJ conversion.
2005 TJ Rubicon.
2011 Grand Cherokee Laredo 4x4, Mrs. LUCDOG's DD.
Lots of parts not for sale, i'm a hoarder.