As you say it runs just the same until it stops after you turn the fuel off, I am thinking a high fuel level is not the problem.
I am wondering now, how did it run before the rebuild? I missed that bit.
For the record; I have had oversized mains affect the idle adjustment on a car, twice now - both times with aftermarket Holleys (a 350 - two barrel and a 600 - four barrel) They would idle with the screws bedded until I put smaller mains in. Having said that, they are very different to what you are working on.
I have also had a perforated power valve give a very rich idle, but I highly doubt you have one of those.
Wisely, you are not neglecting the electrics. Be interesting if something there fixes it.
Finally, I forget now, do you have even compression? (no leaky intake valves blowing back through the carby and picking up fuel twice for that cylinder)
Your updates are much appreciated; we have all had these sort of troubles and I usually learn something from threads like this one.
Don't despair - you will get it!
Jarrod.