Hi, Philip H,
I'm one of the guys over on that Trainboard thread about the Minitrix U30CGs on Kato U30C mechanism.
For what it's worth, the various posts over in that thread seem to imply that while some Minitrix U28C mechanisms run OK,
by today's standards most of the mechanisms are very noisy and prone to electrical pickup problems. At least on that other
thread, many have said that remotoring the Trix is unlikely to produce anything near what a standard (an relatively inexpensive)
U30C / C30-7 Kato mechanism will give you right out of the box. The original run Kato U30C / C30-7 non-DCC ready mechanisms
can be had for not too much given the newer DCC ready mechanisms are now readily available.
If you are dead set on keeping the same shell, you could put it on a Kato U30C / C30-7 mech.
Anyway, hope that helps, of course, please do as you see best, more power to you.