Here's another scan of an old photo. It's me running a Retro Twin, around 1990 (before WorkMates were invented).
When I lived in Paris, and couldn't really run engines at my place(!), I used this stool to run them anywhere appropriate.
This photo was taken at the major French Coupe d'Hiver contest (the original).
What a superb engine. This one was anodised blue, including the (PAW) carburettor body.