There are no threaded holes except for the belt adjuster bolt hole in the front bracket. The pivot holes in the generator end frames are not threaded, and never were. That should be common knowledge for anyone who has worked with these engines on a regular basis. The original-equipment pivot bolts had close-fitting unthreaded shanks through both items, and squashed-thread self locking nuts. Chances are those items have been lost many years ago. A good substitute might be 5/16" Allen head shoulder bolts, or 3/8" shoulder bolts if it's necessary to drill the generator end frame and bracket.
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!