the 65-77 is for the 10 amp generators used those years. The 78-81 regulator is for the 13 amp Hitachi generator, which is currently made of that rare material, un-obtainium. If you still have the Hitachi generator, use the 381-329. If your gennine has been changed to the older style (which is all thats available today) use the earlier regulator.
Faster, Faster, Faster! Till the trill of speed overcomes the fear of death......