Bryce, several options were available for the H50. I'll assume you do not have the smaller H and HS 18 Watt alternator- which is what the majority of us have on our small frame lighted engines. For that, I use six volt incandescent bulbs, because 12 volt bulbs are too dim. (This is what I have used on two different bikes) I would try a 12 volt bulb on the 3 Amp system below, but it might be too dim unless you're at full throttle. For the remaining options, I'd run 12 volt lamps.
Tecumseh 3-11 HP Technicians Manual page 48 refers:
3 Amp A.C. Lighting Alternator
2500 R.P.M. - 8.0 Volts A.C.
3000 R.P.M. - 9.5 Volts A.C.
3300 R.P.M. - 10.5 Volts A.C.
3600 R.P.M. - 11.5 Volts A.C.
3 Amp DC Alternator System - Diode in Harness Sleeve
2500 R.P.M. - 8.0 Volts D.C.
3000 R.P.M. - 9.5 Volts D.C.
3300 R.P.M. -10.5 Volts D.C.
3600 R.P.M. -11.5 Volts D.C.
3 Amp D.C. 5 Amp A.C. Alternator
3 Amp D.C.
2500 R.P.M. - 8.0 Volts D.C.
3000 R.P.M. - 11.0 Volts D.C.
3600 R.P.M. - 13.0 Volts D.C.
5 Amp A.C.
2500 R.P.M. - 8.0 Volts A.C.
3000 R.P.M. - 11.0 Volts A.C.
3600 R.P.M. - 13.0 Volts A.C.