RD,
"I allow for, or make on existing engines, a window in the crankcase whereby I can adjust those weights without stripping the engine." The only thing that comes to mind to say about this is, "that's some gansta' motorcycle mechanics."
KiwiGF,
Got ya' on the rotating vs. reciprocating, but on our engines, as I envision it, the balance factor would be the same regardless of the difference in rod weights. Maybe more obscure (to me) factors, like twisting, bending, etc. come into play, but, as I mentioned, these seem trivial compared to imbalance at combustion. Referring to your excellent post about static balance, the procedure, as I recall, has you hanging a single weight from the journals to test the counterbalance.
If, at any point here, it seems like I actually know what I'm talking about here, that would be a fortunate accident.
Richard L.