As far as I can tell, its the standard axle used in the 6000 series trucks, with full floating hub and what they call the "twinplex four anchor" type brakes, which were first used in '51. This applies to both single- and two-speed axles. The 1-1/2 ton trucks had the same setup, but the GAWR is 2000 lbs. lower.
Have you checked the axle serial number to see if it's the original? The number is stamped on top of the carrier.
A note about the brake return springs on the twinplex setup. According to the '52 supplement to the '48-'51 shop manual, "the identification and proper installation of the brake shoe pull back springs...is of utmost importance." There is a nice diagram in the manual.
