For what Your needs are you could use our A.P.U. unit with the "chopper setup" (air cooled IGBT) Ingersoll- rand Rotary screw air compressor, fit it in the same area as your engine generator and you would be good to go. Hook the outputs up to where the current generator hooks in. Ram switch throttle. SIMPLE to do. Tier4I even. You would even have 480 3 phase available to run equipment, not to mention a good source of compressed air.
Our unit has been starting right up in 10 degree weather with out a block heater. All of this for under 7 gallons an hour at full load.