What happened to the last engine that was in there? Do you have any details for the current engine? Make? Power output? Max RPM? What custom built bits were made to enablle the engine to fit the Haflinger Gearbox shaft? Does it use the original Haflinger clutch or the bike engine's clutch.
Sorry for all the questions, but your post is sadly lacking in details which any propective buyer would like to kknow before making any decision to purchase the vehicle.