G'day Richard75,
A warm welcome to the ODK forums.
We don't appear to have a Villiers Spec Sheet available that covers a Spec Number that high, but the X definitely denotes Australian manufacture. That would have been at Villiers Australia's Ballarat plant. It
may have a date stamp on the flywheel, in the format M/YY or MM/YY.
As this is a horizontal shaft engine, used in many industrial applications, it's probably unlikely that it has a customer-specific Spec No., unless it has unusual features like gear reduction or a non-standard PTO shaft.
It has been suggested in the past, that the bloke at
http://www.vaces.com.au/ is the best source for Australian Villiers parts, and maybe info too.
A workshop manual download:
http://www.nigelpacker.me.uk/Villiers%20WSM.pdf