The new solenoid and voltage regulator didn't do squat (at least they were cheap), so I think I will start removing the wiring harness little by little so I can properly inspect for a short...

 

Got her running good again at last...
In the end I found that the main ground cable from the battery had been rubbing on the alternator and was worn all the way through the insulation. I replaced the ground cable (couldn't get a black one long enough, so bought a red and heat-shrunk it black) and the alternator, re-wrapped the wiring harness and a few tactically placed cable-ties has it going like a champ!
Thanks for the help guys