Thanks, that makes a bunch of sense, and I guess in theory, adding weight may make them less prone to flutter at higher speeds. But I wonder what effect that extra weight would have on them in high g banked turns, or transient high g loads? Just trying to wrap my head around that particular modification.
I think the mod you're talking about is the counterweight on the elevator control torque shaft aft of the cockpit. This weight was added to due to the P-51's tendency to get light on the elevator control during high positive G's. With this weight installed the stick forces increased with the onset of G instead of getting less.
Cheers,
John