There’s not a huge amount of _explicit_ dependency on the bit width of the system in either the 3600 or Ivory. Of course there’s still plenty of _implicit_ dependency in terms of hardware interaction, object layout in memory, collector implementation, etc. but that’s all stuff that had to be dealt with anyway to port from CADR to 3600 in the first place, and then again to port from 3600-series to Ivory.

I was thinking that someone could have rewritten the CADR microcode to run on a 68020+Custom MMU system with no other OS, there isn't all that much of it.

This would be tied to the bit width of the system.