Fuck yeah, got the GTO rewired. Inverted the starter, ran a 2 ga. cable from the battery post down to the starter post, ran a 4 ga. cable from the battery post to the alternator post, then pulled the two wires that ran from the starter post to the harness and put them up on the alternator post instead.
Also topped up the AC, and got it running again. Should probably pull a lead from the pressure switch to the ECU so that it can jack up the idle mixture a little, but it felt good enough that I didn't feel like it was a "must do" right this second.
Also welded and painted the cart for the roadster body, so that I can roll it around on casters until it's ready to rejoin the frame for good and all.