Though I’m chiming in here late, I did go back and skim most of the thread. You have certainly done a bunch, some multiple times, to correct the issue. I commend your perseverance.
I did see cam timing discussed briefly, but didn’t see definitive verification thereof – perhaps I missed it. Some of your symptoms are consistent with bad cam timing and this motor will run when surprisingly out-of-time, but it won’t run right at all rpm’s.
Risking redundancy, here goes:
Remove stator & tappet covers,
Rotate crank normal direction while observing left intake valve,
Rotate until intake valve opens and then closes,
Shortly after closing that valve, continue rotation to next TDC of left piston (TDC compression stroke).
Notably, one should use a dial gauge on piston to determine that TDC and not the XS Charge rotor marks: something weird is going on here and those marks are among the suspects. Absent a dial gauge, fashion a rod to carefully insert in the spark plug hole to verify piston TDC. The hole angle will try to wedge it against the piston crown – avoid that.
Remove the right “points” cover,
Observe the R. cam end and locate dowel pin (or hole) on the cam – it must be at 12 O’clock on a line through crank & cam centers. Also note the T mark on rotor and verify it is correct.
Report results for further pondering.