I wouldn't count on the wheel end gearing swapping. It's very similar, but not quite enough to swap.Oshkosh MK23, 25, 27, and 28 with TAK-4:
3.556:1 planetary wheel hubs which are the exact same ratio as the common AxleTech 4000's. Swappable, I'd say. There's a few noticeable between the internals of the end plates.
1.687:1 R&P ratio. TAK-4 and AT4K diffs look identical. Possibly swappable, too.
5.999:1 overall ratio. I would find a way to lock the wheel hub gears, which would give me a 2.14:1 axle ratio. Stock is 3.33:1
30000 series transfer case. 1.27:1 underdrive, single speed. 32/68 planetary torque split. If I acquired one, I'd open it up to see if the diff can be flipped around. With a rear-engine bus, everything is backwards in comparison to the vehicles that use the drivetrains that I'm considering.
Put those ratios together with our Allison HT740D and loaded Michelins that revolve 491 times per mile and you drop the engine rpm to about 1,300 at 70mph. About 100rpm below peak torque rpm, which I'd call a decent win considering what I'd be working with. Them military trucks are geared low.
Again, I don't think the R&P would swap, but it is VERY close to Axletech 5000's. The 4000 housing is different...
Flipping the differential in the t-case would only flip the torque proportion to the other direction (more torque to the front axle). Rotation direction would stay the same. You could flip the differential housing in the side-to-side differential. This would be easy on a non drive-thru carrier. The drive-thru carrier would require a different housing.
As for locking out the wheel end gearing. It could be done in theory, but your ratio isn't correct. You'd be left with only the ring and pinion ratio of 1.68:1. This would also put a lot more strain on everything upstream of the wheel end planetary. None of that was intended to be transmitting that much torque.