The 48-53 crankshafts use a narrower connecting rod, so the earlier rods won't fit in the slots for the connecting rod journals. A little attention to an early rod with a belt sander solves the problem- - - - Narrow the big end and it drops right in. I've done that when I had a set of brand new, never run military surplus early rods that needed to go into a later model engine. It's running very well now.
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!