New gears in the 40's and 50's had a habit of "wearing in" a little, so the factory setup took that into account. Newer production items probably have the benefit of a little more accurate manufacturing, plus better heat-treating, so they can be set up to the tolerances the gears ended up with after a run-in period.
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!