Roger,I think is the guys name.
Member of the Jawa/CZ Club and Ours.
Bike is a Jawa 500R.
Jawa 350 rolling chassis with Rotax 500 lump squeezed in.
As done by the then importers Skoda UK.
Roger got hold of one of these and modified it into a trail bike.
And a very nice job too.
Jethro