Weren't some Unimogs fully hydraulic, ie pump driven by the engine charges an accumulator and then oil is pumped to wheel motors? This means the wheels stick out below the chassis with no driveshafts, great for standing crops etc.
According to this pumps are 85-92% efficient (probably at their optimum ) https://www.machinerylubrication.com/Re ... drive%20it
Pumps vary a lot, here's a Dowty one, which at its optimum is 94% but falls away to 70% worst case.
https://www.dowtyheritage.org.uk/conten ... lic-motors
So realistically you might average 92% for the pump, and run a big accumulator, and maybe 85% in the motors, to give an efficiency of 78%, less losses in the hoses and coolers and valve gear.
Your next job is to find out the efficiency of a conventional driveline. The diff is very important.