Update: So i recently managed to try my information seen above out, and I can confirm that it works, I made an adapter harness that converts an early 1g dsm /gvr4/3g csm 2 pin wire connector, to the newer 4 pin 2g style alternator pigtail, so essentially you can use a 7g Galant 2.4 or 2g dsm spyder or turbo engine only, the 420a 2g alternators are not gonna work with this, as far as I know, in order to use the newer alternator in an older car you simply get a 2g style 4 pin pigtail you can get them off many other newer Mitsubishi cars the lancers, 3g eclipses, 8g Galants etc, and then locate a 1g male style alternator pigtail, I got mine off of an older mid 90s Infiniti j20, they use the same 2 pin wire connector, it was by the fuse box, for the wiring, you wire L wire to L wire, and S wire to S wire, and delete or simply tape up the other 2 wires on the 4 pin 2g alternator connector, no external regulator was required, I did have to enlarge the charge wire ring terminal because the 2G dsm alternator used a larger M8 charge cable stud vs the 1G which used an M6 one, by making an adapter harness I can now use both alternators on my car, I tested it on a 3g 1.5 csm but it is the same as a 1G DSM, "91-"92 Galant vr4, pretty much any of the older internal regulated 2 wire Mitsubishi vehicles.
To make it stupid simple i made a color coded picture of what wires go where.
pic upload free