Problem(s) solved!
You all were exactly right–it was definitely a bad engine ground despite all my previous testing that suggested otherwise. I cleaned up the extant ground wire thoroughly and I added a new additional but unobtrusive ground strap from the block to the firewall. Engine fired up immediately after that!
But then it started puttering out. Not a fuel issue but more like it was somehow losing its spark. Welp it was. I went through and traced all my wires again very very closely. The wire leading out of the loom (coming from Fuse 4) to the coil’s low voltage - terminal while continuous was badly frayed with almost no insulation left on it right where it came out of the loom (where the loom is bolted to the body right by the front right engine mount). When the engine ran the wire was able to move just a little bit to and fro and this was allowing it to intermittently graze the body and ground out. Of course if that wire grounds out the current just flows right back to ground skipping the whole coil/dizzy/etc. Clearly the ground was my main issue but this wasn’t helping anything.
I spliced in a piece of replacement wire and the engine settled right down and idled! No misses, just a happy idle. Although we are up and running again, I’m going to take the time now to inspect all my wiring systematically and look for any other wires on their way out/fraying! Where there’s one I fear there could be more!
Many thanks to all of you–very grateful for the advice and wisdom shared!
