We are replacing our similar sized two box (fridge and freezer) Grunert system with an AB Cold Machine. I spoke to an AB tech support guy yesterday and asked him about running two evaporators off one compressor. He said that, while it could be done, it would not be a good idea. I didn't cross-examine him as to the reasons. We've decided to use the freezer box for dry storage and to make do with the freezer capacity of the "large" evaporator in the fridge box.
He also mentioned that the only reason to opt for the "super" (water cooled) machine would be if the compressor had to be installed in a very hot place, like an engine room. Since our compressor will be installed in a fairly large area under the salon settee, his advice was to, cut a ventilation hole in the box and install a louver and a small fan to increase circulation over the compressor. Of course, additional insulation for the box would help as well. Also, by eliminating the water cooling system, I can permanently close up another hole in the hull.
Good luck with your project.