The part on the far left of the illustration which bolted onto the block to adapt the transmission housing to the engine was individually fitted to each engine by a set of factory-installed alignment pins to minimize runout. If that adapter ring was attached to a different block, it was a crapshoot whether the block and the transmission would align properly. A dial indicator mounted on the crankshaft hub was used to check the alignment between the engine block and the adapter.
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!