Stand the block up on the base of a radial drill press, with the bellhousing bolted snug, but not tight to the back. Dial indicate the bellhousing hole concentric with the rear main bearing bore or the crankshaft flange and torque the bolts tight. Recheck alignment, and drill and ream for a few dowels- - - -1/4" or 5/16" should be plenty big. Drive a few dowels into the reamed holes and press on.
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!