Thanks again Jim for the reply. I feel a little on the stupid side here. I looked a little harder at the Chevelle after the plug differences and found that it dies have a external regulator. So I will just take it off and replace it as I know there not to expensive. Would a bad regulator cause the low voltage only 12.2 or .3 at the battery when car is running? I was told that it should be around 13 or a little higher when running and reveed up
Sometimes I can be looking right at something and not see it right away. It happens.
The regulator works with the alternator and if the regulator senses that the vehicle needs more power and the regulator does not have the alternator put out more power, then you can have low voltage issues and/or high voltage issues.
When I bought my 68, it still had the original alternator and external regulator on it and the first time I took it out at night I commented to myself, boy the lights are really bright for this old of a car and once I measured the voltage at the battery I found out why the headlights were so bright. I measured darn near 16.5V which explained why the bulbs were so bright and probably why the aftermarket radio was fried.
The external regulator also needs to have the proper signals sent to it before it can get the alternator to react properly so while you can throw new parts at the problem, there may be issues with the car that even with new parts will not get things to work right.
Recently there was some discussion about how the original regulators have the headlights going bright and dim so on my 68 I did some tests and never saw this issue but I did document things and the highest voltage I have had was right around 14.1V or so. The battery voltage before the testing was right about 12.6V. Even if I had a voltage of 13.6V across the battery while it was running I would be happy as from what I have read and seen, you need a minimum of 1V over the batteries nominal voltage so the battery gets replenished and keeps up with the electrical demands such as the headlights being on, the heater fan on,and so on and probably you don't want nothing much higher than 14.5V
As far as a dedicated ground from the alternator case to the battery, engine block, or the body of the car, sometimes this has to be done due to the coating on an alternator to where the coating prevents it from seeing a ground from it being bolted to the engine.