No more than 12.5 charging-Has to be VR problem?

First off, I would like to start by saying I have researched and read a lot of posts about charging issues in the forums. I find the posts by 67dart273 to be more than helpful & thank him for his genius and knowledge in this area! especially the posts when helping Robj with his issues.

My setup/configuration:
>'73 Duster
>New Ultra AGM Battery (tests at 12.69 volts)
>New Alternator (dual field terminal)
>New Painless wiring harness (Thus eliminating amp meter & bulkhead connection issues)
>Volt meter installed to a Ignition run wire
>GM HEI Ignition mod

I have performed the multiple tests and have found a basic 12.48 to 12.58 throughout the system, from key on/engine off to engine running at fast idle. Have found from a .3 to .7 volt loss/drop when checking loss/drop.

Cleaned up grounding points for VR, alternator grounded at VR attached point, engine block grounded to frame, battery grounded to block & frame. I have even tested with a ground wire running from VR/Alternator ground point to battery negative.

I have 3 extra Voltage Regulators laying around plus the one installed in car, so a total of 4. Upon installing the extra 3 VR's I get charging from 12.5 Volts and at fast idle/revving up motor, all 3 allow charging into the danger zone of 16-18+ Volts....so I know the alternator is GOOD as these VR's are bad/junk and let the alternator attempt to overcharge/cook battery.
The 4th VR, when installed, will only allow 12.48 to 12.58 output from charging stud on alternator to battery even with load (lights on)....and Volt meter gauge in car stays at just over 12 V.

I went for a test spin with the "4th" VR installed for about 20-30 mins to see if the volts dropped (thus running off of just battery) and the volt meter gauge stays pretty constant at 12 V or just over. Car starts with no problem after test spin & battery tests back at 12.38 - 12.46.

My question after all this babbling is:
Can the 4th VR be "bad" in the form of not allowing more than 12.48 to 12.58 volts into charging circuit?

I am going to buy 1 or 2 new VR's Monday. Napa is my closest retailer, so will try and get an Echlin VR (as they seem to be the most reliable).

Thanks in advance for anyone's input/advice!