1976 KZ900 Stator Rotor

Hi All,
I been haveing a charging issue with my 1976 kz900 and i think i may have found the problem.
I purchased a new magnet rotor ( part # 21007-1004 ) and on the rotor it has a 8k stamped into it. The rotor that is currently on the bike has a 6k stamped into it. The problem i been having is im not getting over 12 volts to the battery at idle. All other related parts have been replaced numerous times (Regulator / rectifier / stator / harness... etc). When i purchased the bike i'm pretty sure the owner new he had a charging issue.

My question is.... what do the numbers stamped on the rotor mean? Also, is there a possiblity that the original owner had changed out that rotor with one off a different model?

The fsm for the 998c engines says that regulator/recifier output should be from just below battery voltage (at idle with headlight on) to no more than 15v at any higher engine rpm. The voltage should rise as engine rpm does, without going past 15v. Alternator output is supposed to be measured at 4,000 rpm ans should be around 50v.

I don't know the spec's for the 900, but I'd be surprised if it made more than 12v at idle with the lights on.

For the 900 - shamelessly stolen from OMR

Ok... i got the old rotor off the crank. Does anybody know the best way to reinstall the new rotor without damaging the magnets or having the springs or pins popping out? Seems like it will be kind of difficult with the woodruff key.