Those wheels look like they take conical lug nuts. Do your current wheels take conical or flat lug nuts?
If they do take conical nuts they are not "flippable".
Your question on weight - does it refer to GVM? If so, it depends on the tires you intend to mount (13.00R20 XL??) and the placarded axle rating.
I know in Australia a single rear conversion must be approved by the Transport Dept and therefore engineered. What about the UK?
Unimog U500 with Unicat camper; diesel BMW X5 35d, diesel BJ40 Landcruiser and diesel M37