I like Steve's solution best, but my neighbor has a neat set up that he uses for muoltiple things around the farm that needs 12 volts.
He has a '52 Model B that is 6 volts. He put a V-belt pulley on the belt pulley shaft and has it turning a G-M alternator that is mounted below it on a frame bolted to his draw bar. Two 12-volt batteries are mounted in a box next to the alternator. He uses it to either jump start or charge the batteries on farm trucks and other tractors, power a 120 volt inverter, in the summer it sometimes powers a 12 volt electric cooler. In addition, he made an adapter to run his 12-volt cordless power tools, not to mention a radio/tv combo.
To me it is more trouble than it is worth, but he loves to show off all of the neat gadgets he can adapt to his system.
A bored farmer with a nice workshop can be a dangerous creature when he has nothing much to do in the winter months.