Removed Speedometer Gearbox, Need Spacers

1972 cb450, has anyone removed the speedometer gearbox and ring and replaced with a spacer? If so what thickness did you use? Trying not to spend 30 buying something like this - http://www.power-barn.com/honda-speedometer-gearbox-elimination-spacer-kit-for-cb350-cb400f-cb450-cl450-cb500-cb550-cb750/

The ones I make are much prettier but a bit more expensive