Doug.........I don't have enny problem with your converting yer NAA Jubie to 12v.
As for clicking OHV rocker clearance, MORE CLEARANCE is better'n NONE. Insufficent valve clearance will lead to burned exhaust valves.
I just checked yer OHV specs: 0.015 Hot. Usually they allow +/- 0.001 variance (tolerance) from spec. Me? I always adjust for MAX allowable clearance because as time goes by, the clearance closes up. By setting clearances to 0.016, I can go a very LOOOooong time before I haffta reset the valve clearances. And iff'n they're ALL set the same you won't hear one clackin'way.
But BEFORE I started grabbin' feeler gauges, I'd rig up some sort of "stethascope" (lenght of rubber hose) and IDENTIFY where yer suspect "clacker" is located. 'course, iff'n ya gotts time to burn and gotta an ITCH to scratch, and you just gotta tweak yer valve clearances, go right ahead.........respectfully, Dell, a 12v advocate for the right reason