Powering the front axle will be eazy-peazy,,,
Simply design the drive of the pump/hydraulic motor to be a little too fast(10-15%) at working speed.
The front axle has to be designed for a single speed, or else the pump will need to be variable displacement
(VD means BIG $$$$ ,, and hard to operate considering the 10 other levers you will already be trying to move correctly,,
)
The trick will be to use a VERY low pressure, so that the excess flow will simply go past the pressure relief valve .
You can get the power you want by using a large hydraulic motor, and matching pump.
The pressure has to be low (less than 650 psi) so as to not heat the hydraulic oil too much.
So, you need to buy a hydraulic motor that will give the speed and torque you want when operated at 650 psi.
Now you know the pump size (displacement in cubic inches per revolution)
The pump that you select will simply be sized to give the flow needed to rotate the hydraulic motor at the correct speed.
There is no other spec for a single stage gear pump, only the GPM at engine speed.
I do not know of a pump that is not rated for the pressure that you will be using, so GPM is the only spec for the single stage gear pump.
(The higher the pressure, the greater the heating of oil as it goes past the relief valve)
I simply explained the drive system that was used on an early rear wheel assist conversion for a two wheel drive combine,,
that was used to convert the 2WD combine to 4WD at the lowest possible cost.
I read about it somewhere,, but, that was the "pre-internet" era,,
