The 20mm spacer seems an anomaly and dare I suggest provided to offer a one size fits all aspect to the the SSL RS kit. The instructions suggest its location above or below stub axle are chosen to best suit the OE ride height. The main spring pre-load initial setting table then lists above or below spacer location for all models from 4/4 Sport and Kent engines to +8, so clearly its acceptable fitted either side of axle. I did wonder for lighter models if it could be left out altogether with the slack taken up by main spring pre-load collar to acheive zero static rebound spring pre-load whilst allowing higher ride height. One for Peter B maybe?
I've got the spacer below my stub axles to give a low ride height on my 4/4 and it works fine, I never have any bottoming out. I was originally a bit concerned that I might have contact between the top of the tyre and the underside of the wing stay, but it's never happened despite caning it up and down some of the roughest roads the UK has to offer. My engine is pretty light though, so if the Plus 4 engines are heavier it might not work so well in that configuration.
