Thanks again nm9! Ok so if I understand your thinking the rotating mass might be close to the original mass indicating that it might be running ( a 1973 set up) a cast crank which was externally balanced. This is my hunch too but means the HB was totally wrong as I had suspected not only the timing mark in the wrong place which was obvious but it was set up for an internally balanced set up. Also the Torque Converter balance needs to be confirmed through visual inspection.
Correct me if I am wrong here.
Now you brought up a great idea my bore scope IS flexible AND thin and should easily snake up through the oil drain plug! What a great idea. I might be able to find a parting line to capture on the counter weight.