Was the other truck a diesel?
No. I think it was a '94 K1500 5.7L, the same truck I stole the front suspension from, to put on my '88 K1500. I'm thinking the muffler inlet, and the tailpipe are 2 3/4" tubing.
At any rate, it was a single-catalyst exhaust that the Treasure Yard had already cut the catalyst from--so I unbolted everything that would have been behind the cat. Slid the hangers into my truck's mounting points like it was made for it. I cut some pipe ahead of the muffler, and welded-in a Y-tube, which I then welded to the stubs coming out of the twin catalysts on my '97.
No doubt this would not work well under load at higher RPM--but I use this truck to plow snow. "High rpm" is just not an issue for me.