Phil, if you are using the nylon lock nuts on the axle, they are not necessary. The original set ups had those, as there were no lock nuts used and the tightening of the bolt with a lock washer was to hold the whole assembly together, which gave the opportunity to over tighten the bearings if there was no bushing there. I use these lock nuts
https://www.OldMiniBikes.com/5-8-18-j.html
I have made my own bearing spacers from aluminum tube that you can find at Lowes/Home Depot that has a 5/8" diameter