I'd call around local shops if I were you. I called around about mine here in FW and found a shop that would replace mine for $160 - that's installed and the old one disposed of. When you talk to them, tell them it has a thermal sensor that runs into the cat to insure they'll quote you the right part/price.
Make sure you need a ne cat though - get under your truck and shake it. If you hear noise, like little rocks rolling around in there, your cat's bad. If not, it's probably okay - unless you're burning a lot of oil. If you are, I don't think you'll hear the rattle, but the cat will be plugged up and the chem-beads that do the catalyzing won't work...
Before you start throwing parts at your truck - if I recall right, you're trying to pass a smog test - get the factory manual for the smog equipment. Start testing everything and checking your vac lines. I've been going through the same nightmare with my 60 here in TX...the mechanical screw-ups that have been done are amazing (PO, thanks for getting a 'great' mechanic! -please note sarcasm) - my air pump was hooked up wrong, all of the vac lines were routed wrong - and now that I've gotten all of that fixed, I've found that I've got a plugged vac manifold (on the intake manifold) that I need to take out and clean - I'm not pulling enough vac to get the air injection to work right...and so it goes.
I spent about $475 with no headway, got the $20 book and haven't had to spend a dime since then, and I'm getting closer.
If you get into testing and need help, you can call the man-a-fre tech line and talk to Robert about what you're doing. I've talked to him a couple of times and he's really knowlegable and doesn't try to sell you parts you don't need. (he's the guy that told me to check out the vac manifold and how to test it, etc...)
