Terry Robinson originally developed the Slomo based on trials carried out on his own Roundhouse Billy and then moved on to Katie and Darjeeling B. The thing that these locos had in common was that they all ran on 45mm track and all had non-insulated wheels, so it was a bit of a surprise when I came to try to fit one to my 32mm gauge, insulated wheel Katie. It didn't fit!
I got away with just replacing the rear wheels with non insulated replacements from Roundhouse. The grub screws on the front wheel bosses did foul the flywheel, but I manages to shorten them so that they just cleared.
The Slomo fitted to my Katie does not have the benefit of the rubber mounts which reduce noise transmission, but it sounds fine to me!
I am still learning to drive Katie and it is huge fun - just like the real thing! Please note that katie is fitted with the standard r/c regulator - and be amazed!