Use the distributor as a reference- - - - -the priming shaft needs to be at least as long as the distance from the end of the shaft to the top of the distributor housing. It could be three feet long and it would achieve the same result. I usually grind a 3-cornered flat area on the drive end to keep the drill chuck from slipping under a torque load.

"Common sense is pretty uncommon these days" ! I don't know who said that, but he was right!
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!