Hard to say. It depends on what they did to get the higher output. Sometimes to get the higher output, companies test at lower voltage. Other ways include using a more windings - which in turn draw more current resulting lower output at low rpm. In theory, if they could fit things more precisely, then the rotor's field would be closer to the stator.


No.
If you wan to use the regulator on hand, then yes the second brush is grounded.
Your car came with a positive controlling regulator. This means the regulator controls how much current, if any flows into the rotor.
Starting in 1970, Chrysler started equiping all the cars with a negative controlling regulator. It uses the voltage reading on the positive feed wire to control the negative (ground) connection of the rotor.
The question is whether your regulator can handle the current draw of the either the squareback on the car, or more so, the Powermaster. Maybe Powermaster will tell you the current draw. Good luck on finding a person at a VR manufacturer to say what any particular one can handle.
It depends on where the fans are connected in, and whether the fans will be run a lot on battery or not.
If you just neeed to get a race, or a couple weeks, you could connect the battery to the alternator output with an 8 ga. But to protect the system, put a 16 ga fusible link between the battery and that wire.

My suggestions longer term are:
A. Go back to mechanical fan, with shroud, etc. Then factory wiring scheme works pretty well.
B. Keeping the electric fans, go to a longer more efficient alternator like the Denso and alter the factory strategy. I think I would use an auxillery fuse/breaker box and relays, with one of those relays allowing a direct connection to the battery and alternator. Also I wouldn't use an AGM battery. If its getting drained from running the fans with engine off, then it will draw a bunch of amps when recharging - and an alternator that can supply a lot of amps at low rpm will cook the battery.