Hi,
the 250 side pipe engine numbers start 980.02.****
the id plate manufacture date will only have the first 3 digits , ie; 196 or 197,the actual year was never stamped at the factory, brand new id plates are available online,
the frames and engines, forks brakes wheels are externally different to the later 71/72 250 yellow tanks, similar but not the same.
cheers