Found this on Tbay. Anybody know what its for or how it works? Starter or generator tester? http://r.ebay.com/hlYB20
It looks like you would mount an electric motor on the other end of the plate to turn the generator show and check if it is producing amps on the gauge. Beyond that I don't know.
With a motor attached it would serve as a 6V source for charging batteries or supplying any other load. I have something similar using a Delco 6V generator with an adjustable field...was very useful 50 years ago as a variable voltage source.