At my wit's end

Can you get a FSM for a 73 Dart? It would cover your current 1920 carb in a lot of details so you can be sure stuff isn't missing or installed backwards. And I have to ask, why not swap over to a factory electronic ignition? Your points distributor's shaft bushing may be worn out, after years of having the pressure of points rubbing against the center cam, causing the whole thing to wobble. A factory electronic distributor, even a used one, will most likely not have that problem. Yes it's more stuff to swap over (wiring harness and changes to it, ecu, etc.) but it works, and can be taken off any 73 and later non lean burn slant six vehicle. And if you have a manual it can be used to troubleshoot it.
The 1920 is a good carb. I'd check the throttle shaft for slop - if there is any it's a potential vacuum leak source. It can be re-bushed, or in a pinch, the carb can be disassembled and you can center punch all around the shaft opening to tighten it up some. There's also nylon strips in some rebuild kits that can be inserted around the shaft and the housing to tighten it up some.
Your pine sol dip may have worked well to clean it up. Did it also strip off any of the yellow anodizing?
Some guys on here mentioned checking your charging system. On any old mopar of that age I always check the connections from the alternator and the battery that go thru the bulkhead connection at the firewall. They are usually green and can cause problems. The male connectors can be removed from the plug by pushing them sideways parallel to the connector ( --- <-- push this way...) wire brushed, greased, spread back out and pushed back in. Look at the heavy black wire from the alternator and the heavy red with the fusible link from the battery.