"I'm thinking this is most likely a wiring problem, as the fuel pump will prime with no issues when it dies. Maybe it could be a bad SBEC, since this is the one which was in the fire. I guess I'll have to find out soon."

I would leave that parked with the battery disconnected for now if I were you...

I had a harness that had "ghosts" and one night I dropped the hood shut
a few seconds later smoke started roaring out the front opening to the power module..

it was a good thing I'd stayed in the garage and not turned to go in the house