Help with a miss and voltage drop

the 850/650/18*timing, idle throws up a redflag to me.
I'll just bet you the transfers are nearly closed and you're probably idling on the mixture screws alone.Too much idle-timing will do that. It's not too much for the engine, but rather too much for the carb.Fix that first then maybe it faith-heals.I would target an idle speed of about 550 in gear, even less, if the compression is good.
I would expect the TC to drag the idle down only 50 to 100 rpm.

Most ignition systems will be fine down to 10 or 11 volts.
Look for an A/C component coming out of the alt.