Well, I threw on the air rail and pump, finally got the right sized belt and took it back for a re-test yesterday.
They remembered the truck and I could see them looking it over extra well to make sure I had put the junk back on. They seemed to be happy. The lady started doing the test with the magic RPM detector (seriously, how does the one work where they don't attach to the spark plug wire?) and wasn't getting a good signal.
She switched over to the lead on the #1 wire and was having trouble getting the idle low enough for the test. Finally she just gave up. No asking me if there was a trick or anything, just said it was failing because it idled too high. I not-so-calmly explained that it was a 35 year old vehicle. It has a mechanical connection to the gas pedal and if you gently pull back on said pedal with your toe, the idle drops to a nice low 600ish.
She said she'd see what they could do.
Another dude comes over, I explain it to him. He says, "show me." Fair enough. We fire it up, I toe up on the pedal and the RPMS drop and stay low. He says he'd give it one more shot, if it didn't work they'd have to fail it. ok!
5 minutes later I was rolling out with a pass stamp! WOOHOO!
Thanks to everyone on here for your suggestions and parts. I'm sure it won't be the last time but at least now I can get plates and drive it.