Farymann 43F Diesel Governor speed modification help needed.

[90cummins]

I have 2 Military surplus MEP-952b 28v DC APU's 1 of which is being used to support my battery backup system.
These units use a German made Farymann 43f diesel engine rated at 15hp to drive a 280A DC generator.
I'm looking for anyone with knowledge that can help me modify the governor for steady state operation at 2000 rpm from the original 3000 rpm.
Another option would be to information to build/install an electronic variable speed control system.
The reason is to reduce fuel consumption when being used for battery support at lower power levels.
At less than full throttle operation the governor allows excessive droop when a load is applied.

Any information would be greatly appreciated;

Thanks 90cummins