This engine was made in England by Roger Taylor, who was a frame builder and engine tuner.
Whilst being all Jawa, Roger used a crankcase of the latest type (normally fitted with a SOHC 4V head) but opted to use the older DOHC 4V head from the model 895.
The engine was used in Longtracking, but also was used in a 500cc European style Sidecar for Grasstracking.
Pictures and information courtesy of Ben Ludolphy.