You should be fine. Your AC voltage may actually increase with higher rpm. I think having a bad ground may be big contributor to your bike not even charging. With the lower AC voltage you will still get some charging allowing your bike to be ridden and not die on you.
Put the new reg/rec on with a better ground. Fire up the bike and measure the DC voltage at the battery at idle and 3000rpm.
You want above 12.6v DC when your are above idle.
