What voltage is the generator producing? Tapping gently on the voltage regulator sometimes jolts the regulator back to life. If it does, replace the regulator. Are the battery terminals clean and are the cable clamps tight? Six volt systems are very susceptable to loose clamps and corroded battery posts. (Good to be raised with the old stuff!)
It is putting out nothing. Have gone through all your suggestions and it will not put out. From my understanding these shunt generators were simple and very reliable. I have found a shop manual for 46-48 all models and I guess a rebuild will be in order.. It runs beautifully other than not charging...
Check for worn and or no armature brushes in the generator. If you pull them, or what's left of them, look closely at the commutator. The copper segments should be smooth and have no copper between segments. The commutator will likely need turning in a lathe anyway, then grind the kerf off a hacksaw blade and cut between the segments. Now, oin a lathe, smooth the commutator with fine grit emory cloth, pop in new brushes, and it shoukld be OK. Check for field coil continuity also.
There should also be procedures in order to set the field generation through the voltage regulator, basically there is a grounding procedure to get the thing to charge properly. Been years since doing it, but they don't charge until they have this procedure done.