The Hydra-Matic adapter ring that bolts onto the back of the engine was matched to the block for minimum runout at the factory, using a dial indicator mounted to the crankshaft hub. If a different block was fitted during maintenance, it was necessary to check the runout and correct it if necessary, using offset dowel pins to minimize the runout. The Hydra-Matic fluid coupling (not a torque converter, BTW) is very sensitive to centering. My father's independent shop was the first one in Nashville Tennessee to work on automatic transmissions, back in the late 1940s. A few years later, a former WW II tank mechanic who had worked on the M51-A light duty tanks with Cadillac flathead V8 engines and Hydramatic transmissions opened up a competing shop. The tank had two engine/trans assemblies, one for each track.

www.curbsideclassic.com/blog/auctio...c-engines-and-hydra-matic-transmissions/

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