my NHC parts manual shows three different charging systems.
two are mounted to the oil pan,and one to the cowl.
i have a 74 nhc on site, it was in a owatonna skid loader.
it had the synchro 20 amp system.
this has a regulator, and rectifier mounted on the panel on the oil pan.
you HOPE you do not have this one(a VERY spendy system)
good luck. boomer ( the small time onan guy, that sells used parts)