How much of this is original

[motto (RIP)]

Yes, the rear bogie appears to be all original and all there.
One of the reasons these trucks were preferred over the CCKW was that the gearbox is a four speed, 1:1 in top and the two speed t/fer case is also 1:1 in Hi range. The CCKW used a five speed transmission that was overdrive in top then cancelled that out with a reduction in Hi range through the t/fer case. They used more gears, bearings and complexity to achieve the same result.

David