Went to about four different stores today on the way to/from work, and got the pieces I needed to rerun the "always on" 12v wire (yes, it was the original yellow one, and it was so old that the insulation cracked when I bent it). At one point, the insulation had been heated or abraded away by something, and this seems not very recent, as the copper was well-oxidized. Seeing that is what determined me to replace this line.
So, a 3' length of 8 gauge 19 strand, one small ring terminal for the junction block side, and one 3/8" ring terminal for the solenoid side, and all was in order. I gently refit the starter to see if that fixed any issues, and glory-hallelujah, it fired right up. A little love and a few secured connections, and away it went.
"But Parkman51," I hear you ask, "What about that broken junction block? How did you get it working without the new one having come in yet?" Well, with another of my patent 'if it's stupid and it works' stopgaps. Observe the Junction (Literal) Block.
Anyway, now that cranking the engine is back on the menu, I can return to my old nemesis, the FUEL-PUMP. Hopefully I'll have some updates on that front for you tomorrow, but we shall see.