Am I imagining things or is it turbochraged?
Can't figure the carb setup and the gear lever looks like it has rather a long throw. Breather setup into the dipstick hole is different as well.
Leading link forks, disc brakes and a turbo would make for an "interesting" rider experience.
Possibly some German "custom" shop, the German custom shops seem to specialize in producing machines with a singularity of function i.e. death of the rider.