IIRC, the difference is in the angle of the inlet and outlet ports. Somewhere along the way, the ports got moved to a 45 degree angle from their former straight in and out position for motor mount clearance- - - -possibly in 1958 when stovebolt sixes started using side mounts instead of timing cover and bell housing mounts.
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!