I spoke to Graham Potter yesterday (the UK UMM expert), and it turns out that the front axle on my UMM is a heavy duty type, similar to the DANA 44, but possibly made by GKN. That is why the steering arms have two holes on both sides.
The rear axle looks like it is the heavy duty axle too, as the casting appears to have substantial ribs. Possibly also made by GKN. According to the parts list, these could be the type “D” axles, only available in the 5.38:1 ratio.
As can be seen, they are quite rusty on the outside. I will probably remove the axles from the vehicle, and have them shot blasted at some point.