I was able to fit 20/36 gearing with a Feigao 540C 7XL without any rubbing.
Ok, I have a NIB 40t spur handy so I will give it a try tomorrow. Thanks for the info, a few teeth off the spur should help the top speed! Bet it was fast with the 20/36 gearing! That will save me the cost of another pinion gear!