489,741 or 742, the Difference?

Something I found interesting,, is that further down the page on the 2 sites that Swing69 and Cazbah362 use for reference,, is a list the apps for the diff/axles..

64 Max Wedge 53-1/4" Parts Manuals list four different axles for this housing:
2070573 - 741 case w/o SG 30-1/2" overall;
2404003 - 742 case w/o SG 30-1/2" overall;
2070695 - 741 case SG 30-7/16" overall;
2404050 - 742 case SG 30-7/16" overall;

741 behind the Max Wedge..