The dernys I've trained behind on the track that had rollers attached were identical to the dernys they were using in competition at the Ghent Six Day (late 1980s/90s). They were not modified motorcycles. I thought at the time that they were Derny-branded dernys and I can check my photographs to see for sure. But they were the standard derny shape for the time and bore no resemblance to motorcycles. And some of them did indeed have rollers fitted to the rear. As I said in a previous email, Hilary's information suggests that this must have been an aftermarket modification.
--Mitch Harris
Little Rock Canyon, Utah