Once it's threaded, replace the tap with a bolt the same size as the thread you just made. The bolt isn't going to break. Clamp some vise grips or a C clamp on the flywheel to keep the crankshaft from turning and turn the bolt with an impact wrench. The bushing WILL come out! I usually use a 5/8" NC (coarse thread) tap. A NPT (pipe thread) tap is tapered, so you're probably not bottoming out in the crankshaft counterbore.
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!