You cant really use the plug with that adjuster without machining the plug down so it is the perfect length that the adjuster sits flat against it with very little to no gap. If you install spacer without cutting it down the secondary will be allowed to float and the big washer behind the adjuster can fall down in the gap which would prevent the helix from returning all the way. You can duplicate what im talking about by bolting everything up with the plug and adjuster. Open the clutch so the belt drops down in it and now it will be able to float. You will see what I mean about the washer potentially dropping off the threaded portion and preventing helix from fully returning.. If you are concerned about the bolt loosening you can add a normal lockwasher to it or stop at a hardware store and ask for some nord-lock washers......those do an awesome job at keeping things snug.