If I understand your question correctly, you are giving up on the icebox/fridge that is built into the cabinets and want to go with a separate fridge unit?
If that is the case, the only standalone unit I know of that allows remote mounting of the compressor is the Isotherm
. There may be others but this is the only one I know.
I would not recommend mounting the compressor, especially an air cooled unit, in the engine room. Any time you run the engine it will get very hot in the engine room and can stay that way for a few hours, dramatically reducing the efficiency of the compressor.