Hi Nick. That will be just a sequential serial number for manufacture. Have a look on the back of the gearbox, on the gearchange housing at the bottom, usually there is a little aluminium disk there with the model type stamped on it.
Otherwise, take the bellhousing off, and you will find the same model type engraved on the back of the crownwheel. If its a 369 type, you will see it stamped on the outside perimeter edge of the crownwheel.
