That's a 1983 XR500 bored up to 600 with a Mahle piston, 1983 CR125R rear frame, saddle, swingarm and WP shock. There were two in the Dutch Trophy Team. One piloted by Gerrit Wolsink (captain) and one by Simon Schram. In my first video of the 1993 ISDE you can see a close up of Simon Schram his 1983 race bike. Regards, Dries62