Unfortunately it will be extremely difficult to put wheels on the fiddle yard and actually roll it around with stock on as the floor is very uneven. It is possible to put wheels on the fiddle yard however the legs will be higher on one end compared to the other. I fear if I tried to move it with rolling stock it may roll off the fiddle yard or the fiddle yard may topple with the uneven floor. Regarding running older stock on new track, I have ran various 1970s locomotives on peco and Hornby track and they work remarkably well on them and I have had no issues with points on other layouts I have tested them on. I haven’t tried them on code 75 but from what I have been told here and by others, the flanges are too large and sit on the chairs.