I know of a SC 500 that had been converted to water cooling and the motor was put in a Bultaco frame. it also had a sidecar on it and was the only known watercooled converted SC500 in the southern hemisphere in the late 70's. the owner was a real wiz with 2 strokes. The bike won the 24 hour trial sidecar class twice in the late 70's and was the only 2 stroke outfit to win until 94 when a CR500 VMC won.
im sure ive got photos of this yamaha. might put them in sidecar section. ive got one photo on computer but i will have to search for it.