I've had various torque converters get stuck in the crank pilot. When you remove the converter bolts, the converter should slide backwards about 3 / 16" using hand pressure.

If the converter pads are tight against the flexplate, give the converter a push rearward and see if it moves.

Also when reinstalling the trans, put a bit of grease in the pilot to prevent fretting and the eventual sticking.

If the snapped off bolt has any sort of shoulder and that could be what's holding the converter to the flex plate, grind the head off rather than drilling. Once the head comes off the bolt will unscrew by hand, if locktite is used heat the bolt to ~ 300* F to soften the bond.