If the tractor is a positive ground system it will have to be switched to a negative ground polarity.
To do this reverse the battery cables, reverse the amp gauge wires (negative ground = negative terminal on the coil going to the distributor)
If equipped with lights change the bulbs to 12 volt. You might consider a 0-60 amp gauge as most generator gauges stop at 30 amp.
Attach 1-wire from the threaded stud on the rear of the alternator and run it to the amp gauge, run a separate wire from the other amp gauge terminal to the positive side of the battery. When initially starting the tractor rev the engine to approximately 850 rpm to excite the internal regulator, the system should start charging.