What year ford van came standard with positive traction?

No Ford van ever came standard with a system called "Positive Traction." Ford used various names for its limited-slip differentials and traction-aiding systems over the years, such as Traction-Lok. These were *options*, not standard equipment, on many models and across various years. To know if a specific year and model had it, you'd need to check the vehicle's options list (often found on a sticker inside the door jamb or in the owner's manual).