I've been meaning to make these for a while , the idea being to be able to use later Yokomo wheels on the YZ-834Bb and to add a little to the track .
They are an 8 mm spacer that slides over the original drives , this adds 2 mm per wheel , 4 mm overall to the track , they screw on to the original drives and have new threads for wheel attachment , this makes it easier to fit wheels without having to align the holes and also preserves the threads on the original parts .
I can now choose the modern rubber of my choice

, please excuse the rather rough re painted wheels in the photos I picked them up very cheap to play around with for fit.

If a jobs not worth doing then its certainly not worth doing well.
A problem shared is a problem halved but an advantage shared is no advantage at all.