Hi Doug - I don't have a problem fitting wheels on the axle, but rather it the wheels I fitted. I made them myself and, when powered by the previous 12 - 15v motor, there wasn't an apparent problem!
Since fitting (the quite excellent) small motor/gearbox assembly and going for battery power, I tried it out on a R1 curve and points set-up. Having altered the back to back to cope with the R3 points in the garden, I was loathe to alter it yet again for the trailer set-up.
It has quite a long wheel base for R1's and, although it does negotiate everything, there is a very noticeable slowing down (near stall) on the curves. Maybe smaller wheels would eliminate the binding and it would run a little slower (and put less strain on the worm and wheel)
I do intend to make a shorter one (maybe this winter). I take on board what you say about Slater's wheels as they also look exceedingly good as your modeling demonstrates!