Okey, here's the skinny for anyone with a similar question now or in the future.
Factory (Carol) called back and, like MikeH noted, they are now installing Norcold NA7LX (2-way) units on new PC's.
Although listed as a 7 cu.ft. frig, it is really only 6.5 cu.ft. and Phoenix is installing it in the same size opening as the one the N621 fit into, so (yay!) no cabinet modifications are needed.
Important to note: The slightly larger frig does require you to order a trim adapter kit for the door panels if you want to save $$ and use your old door panels rather than ordering new ones.
Again, thanks for the help and input.