Well, I just to make one more post. I kept thinking about it, and decided that what bit needed to damp out the oscillation was not more weight (which affected the accuracy) but more resistance to movement caused by sloshing.
So, thinking outside the box, I found a piece of bronze wool, and attached a golf-ball size piece to the float using a fishing swivel. Well, that did do the trick. Little or no weight, but the bronze wool slowed the movement of the float drastically.
This option cannot affect fuel quality or flow - the pickup is enclosed in a mesh "sock" and feeds the tank-top outlet pipe. Worst case, if anything were to fall off the float, it would go harmlessly to the bottom of the tank.
Case closed.
