Regarding a port to NCR Tower 32 (aka Unisys U5000) mentioned in
        http://www.netbsd.org/Ports/#suggested-m68k
and occasionally on the port-m68k list:

I once had a U5000, complete with a large stack of documentation.  As
I recall, the MMU was not a standard 68851, but something custom-
built.  I don't remember the details, but my conclusion was that it
wasn't suitable for paged virtual memory.

-- 
Lars Brinkhoff          http://lars.nocrew.org/     Linux, GCC, PDP-10
Brinkhoff Consulting    http://www.brinkhoff.se/    programming