Distributor Bolt question

That is a tapered bolt as you observed and is not right for that spot. Somebody put in the wrong bolt. If it has stripped the threads out, then it's time for a Heli-coil insert.

I believe it should be a 5/16" x 18TPI bolt. And if you tap into the hole, IIRC it is blind and does not open below that flat area, but check; if it IS a through hole, be careful to not let chips get inside the engine.

Good for you on the fire-up!