727 and 904 have the same gear ratios (2.45 low) up to late '70's or early '80's. then the 904 was available with a 2.74 low gear. That's also around the time when they started using lock-up converters. The lower first gear tends to help acceleration in lower HP/torque and heavier vehicles. There is a way to tell if the internal parts are 2.45 or 2.74, but I'm not familiar with the details.
Chrysler tested the 727 vs 904 in the '70's and found that, with all other specs being equal - i.e.: car weight, engine, converter, etc., the 904 was faster by about .15 in the 1/4 mile because of the lighter internal parts and less friction.
