You'll need a lot more power than a drill motor to test the output. The 1/2 HP motor on my lathe struggles to do any voltage testing on the checking fixture I built, and it's not able to do a full current check- - - -not enough torque. The Sun generator/regulator tester I used to teach charging system maintenance with for several years used a 2 HP electric motor. I'd suggest a small HP gas engine- - - -maybe 3 HP or more. Wire the test fixture up with a regulator and a battery and be aware that any adjustments you make with the cover off the regulator will drop slightly when the cover is replaced due to better magnetic conduction of the steel cover. PM me if you want to discuss specific testing and adjustment procedures- - - -I've been doing it since the early 1960s. In 25 years or so on the stovebolt site, I've only known two members who have been willing to go to the effort to listen to my advice on testing DC generators properly.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!