Great to see the MLU fraternity diving into this mystery!
From what I know and what I read here I'd say this vehicle is at best a post war military conversion of a GMC DUKW, but much more likely a postwar civilian conversion using some CMP components.
After WW2 in the Netherlands, many GMC CCKW trucks were converted for civilian use to haul dirt/soil. As the load was at least doubled, frames were strengthened or replaced, diesel engines were fitted and axles were replaced by CMP GM C60X axles as they are stronger than the original GMC axles. I suspect that is what happened here.
A number of Italian military vehicles had a steering wheel on the right to cope with driving conditions on narrow (mountain) roads, so that may be a reason why this vehicle was converted to RHD if it is of Italian origin.
There must have been a solid reason for this conversion, it is too much work for a "folly" or an April's fools joke.
