An inversion may cause the mast to fill with water, and depending on
the diameter and lenght of mast, the the leverage weight at or near
the masthead would be significant. I think 1square foot of water is
about 64 lbs. Or about 1 gallon of water is about 8lbs...

Cubic foot. One square foot of water has a weight of zero.

Anyone know what the leverage force would be needed to lift 64lbs at
30ft of leverage from the folcrum point? That may not be exactly the
right question...

Approx. 3000Nm, but that's irrelevant:
Assume inversion. The mast will first be underwater. Then the water in
the mast has neutral buoyancy. To get out of the inversion, the
boat uses hull shape and keel weight, if not a racer designed to
remain stable in an upside down position. But these have escape
hatches on the bottom.

Once the mast is parallel to the water surface, the keel has the best
angle of attack to righten it. Much more than during strongly heeled
sailing, i.e. a few gallons of water at the mast top won't do anything.

Not even a few hundred pounds. If you want easier proof: You can hoist
a person up the mast of even small keeboats witout inverting them.

Chris