What is the current flow when the gauge is pegged? Until you put an accurate ammeter in the circuit, all the hand-wringing over the dash gauge is wasted effort. It's entirely possible the generator is working right, and the gauge is lying to you. Testing a charging system without an ammeter is virtually impossible. A fully-charged 6V battery with a terminal voltage of approximately 7.5 volts supplied by the generator should be getting a charging current of about 7-10 amps, maximum. If it's flowing more current than that, the battery has internal resistance problems.

If you determinre that the battery is OK and the ammeter is the problem, you can reduce the current flowing through the gauge (and the needle deflection) by attaching a shunt to the back of the ammeter. Use a piece of stainless steel hose clamp material bent into a horseshoe shape, drill a hole in each end, and bolt it to the back of the gauge under the wires that are attached there. This will reduce the amount of current flowing through the ammeter by providing a paralell circuit, but the gauge will still register charge and discharge- - - -it just won't go full scale either way.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!