need help

JB Weld on the carburetor sounds absurd. It doesn't even resist gas. Feel free to flame that bozo on Yelp. He might have been endangering your life.

You can get a new 1 bbl carb fairly cheap on ebay (~$50) if you keep looking, or a member here could probably sell a proven one cheap, since so many upgrade to 2 or 4 bbl. I agree it sounds like a "hot gas" problem. An easy fix would be to wrap thermal shield around the metal tube where it passes over the top of the engine. You can get that at most auto speed shops or even regular shops. The carb spacer would help a lot too. Post a photo of your engine bay. The shaking you feel at idle is probably running a bit lean, which could also be from the "hot gas" issue. A popping sound from the exhaust at low throttle (slow) is often due to spark timing. Have someone verify that the vacuum advance rubber tube is connected to the proper port on the carburetor, and test that the diaphragm holds a vacuum (use a hand pump).

Ditto that you can probably find a FSM on-line. Chrysler can't complain since they no longer sell them. The Haynes manual is also pretty good. I found one "Chrysler RWD" in a thrift shop cheap or search for "Dart" on Amazon or ebay.

If the sound you hear is high-pitched, it is probably just sheet metal, which is not a big concern. It could be the dust shields on your front disk brakes (most cars had in 1975) or the heat riser shield around the exhaust manifold. The later especially since you hear it as the engine is warming up. Deep, thunking sounds are of more concern, whether from the engine or the suspension or wheels. It is also common for an exhaust pipe or its hanger to slightly bang against the frame and make a scary (but benign) sound. A wheel coming off would usually be due to a bad bearing, but that will make a squealing sound first and the wheel would wobble a lot before it came off. I think it would also have to be missing the cotter pin so the nut could unscrew. I have had wheel bearing totally fail and wheel stayed on. Ball joints can be totally worn and still not make much sound except when you go over railroad tracks or speed bumps. Same for control arm bushings. If you jack the wheel off the ground and pull it all ways and feel and see no play, both the suspension and steering are probably fine.

The unfortunate part of buying a used car is that you don't know the history. Therefore, you end up checking things that may be perfectly fine, and changing fluids just because you don't know. Most brake shops offer a free inspection, which should include the wheel bearings. They usually try to scare you and upsell you, but only if you are naive. That would be the first thing to check for peace of mind. Don't let them sell you new shocks unless you really need them (car keeps bouncing after a speed bump).