Not too long ago, I bought a '94 Dodge Ram 2500 4x4 utility-bed truck with the 360 gasser. One of the reasons I bought it was because of all of the work the previous owner had done. New engine, new transmission (AAMCO... ugh), new cat, new muffler, and some other stuff. I didn't think I was buying a project, but oh well.
I have the receipts for the work, which basically guarantees that I will never go to those shops. I've only had it a few months, but the weld at the exit of the cat completely disintegrated, and the muffler (Flowmaster copy) actually fell off when its welds failed. The outlet of the cat is right on top of a crossmember, so to weld on it, I had to disconnect both pipes from the manifolds and pull the entire assembly out where I could get to it. I welded a nice piece of galvanized fence post on to it, and re-installed. Then I went looking for the cheapest muffler I could find locally (no time to wait for mail order), and got a Cherry Bomb glass pack. I drove it for a couple of weeks with just the muffler on it, since we have been working long hours at work and I haven't had any time to finish it until yesterday.
Rather than continue welding galvanized pipe, I went to a muffler shop and bought a stick of aluminized pipe. I was just going to angle it out in front of the rear tire, but the existing tailpipe was actually in pretty good shape, so I got a reducer (not sure why a stock 360 needs a 3" exhaust), and welded one end and clamped the other. The mount was in good shape, so I cut it off of the old pipe and welded it to the new.
I'm pretty happy with the result. I spent under $100 including the new muffler, and while my welds aren't too pretty, they look at least as good as the work the "professionals" did before. It's also quieter than I expected, which is a bonus.
Experts are often wrong, but rarely in doubt.