GM never made a true 1 wire alternator, those are aftermarket GM alternators with special regulators built in. What I did on my conversions was use a alternator for a 1979 monte carlo or anything GM in that era. GM was using their first internally regulated alternator at that time. You just have the large stud that goes to the battery, and a plug with two smaller wires. You can get the plug pigtail aftermarket or at the parts store.
On the plug the alternator is labelled 1 and 2. Terminal 2 just takes a very short wire and is jumped to the large output terminal that goes to the battery. The internal regulator uses this for voltage feedback/monitor
Terminal 1 is what brings the alternator online. This wire is run all the way back to the dash. Go to the store and get a small dash indicator light, one that has a plastic socket with two wires. Do not get one that is metal and grounded. Punch a hole in the dash and mount this light. One of the light wires will go to the wire to terminal 1 on the alternator. The other light wire will go to ignition on hot.
When you first turn the key but do not start the tractor, the new dash light will light up. When you start the tractor and the alternator starts producing power, the dash light will go out.
Just remember you do need to change the ignition coil. And of course use a 12v battery and put the negative on the frame of the tractor, not the positive. The alternator is setup for negative ground. The 6v starter works great on 12v. You can also change the headlights to 12v bulbs, or one of the tractors I converted the guy was cheap, so I re-wired the old 6v headlights in series so they would work on 12v.