High volts
Where you said that several batteries have been installed, I don’t think you have a battery problem which will cause over charging.
Most often voltage drop in ignition and regulation circuits cause over charge problems. If voltage regulator is seeing low voltage in harness it will boost voltage output of alternator by the difference from normal harness voltage. In other words if VR is reading 12.5 volts, and battery is at 14v, alternator will add +1.5 volt to 13.5, and charge at 15 volts which will boil a battery dry, and kill it.
You need to check for voltage drop in ground side of ignition circuits, and plus side as well. Ground side should show no voltage drop, and plus side no more than a total of 0.3 v.
Corrosion at any connection, bad conductors, loose connections, and worn ignition switch adds resistance to circuit which causes drop in voltage. There will be a small voltage drop at each of the above that all add together to make one large resistance. You need to sniff out, and eliminate as much of this age related resistance as possible by cleaning, tightening, and replacing conductors as needed.
Well, I said several batteries have been installed, but I didn't R2 the batteries for funsies...it was because they were cooked and no longer could start the car. Needless to say, I don't fancy buying batteries...they're a little pricey. And I had to replace a total of three batteries in one week including other vehicles. My Scamp killed one, my F150 was due for replacement, and my better half cratered the one in her Bimmer.
Not that you needed or cared to know about all that ;)....anyway:
I checked the voltages at the VR (blue wire), at the alternator (blue wire, and charge wire) and at the battery.
@ VR = 14.5V
@ alt (sense) = 14.2V~14.5V
@ alt (charge) = 15.1V~15.4V
Also checked resistance from VR to nearby chassis ground, at (-) battery terminal, and battery (-) to chassis ground. Resistance from VR to ground was < 1 ohm, VR chassis battery (-) was ~40 ohms, batttery (-) to same chassis ground was ~40 ohms.
Another item of possible interest: Before I did the Magnum engine swap, I used a Powermaster 75A alternator, with the same wiring, same regulator (same type anyway), and same battery (before it cooked) and my volts were never above 14.2V at the battery. If you're wondering why I swapped back to a standard alternator, the PM housing was too big to fit against the heads on the Magnum, and of course, you can't reclock the housing. So, that leads me to a logical question: could the alternator itself be suspect of overcharging due to wrong internal components?