Hi,
The supplier of Acto-power motors has already gone bankrupt, so please never forget every Acto-powers has fatal cooling problems if you change genuine rotor into other.
TZ, BZ and RZ are using just same cans and magnets. I think so.
but stopper rings are different material and only stand-up brush version has a steel ring.
and it seem steel ring give much torque as you know.
By the way,
I chose RZ as training motor. (because I love its red graphic.) but it became soon a junk.
first, I had to disassemble also junk TZ to transplant its brush holders.
After assembled I shaved endbell's nipple, and my RZ changed adjustable.
Of course I changed also a couple of its metal bearings to ball bearings.
Last Sunday, I cleaned commutators of various used rotor which came from my junk yard up by lathe, to put into my excentric RZ.
After all, my RZ has adjustable endbell and stand-up brush,
and 12T-rotor inside.
I could get new motor in totally cheap and it's my personal Tamiya Ecology Movement too.