No.4 Mk2 ...
Besides Long Branch, it should be marked No4 Mk1* on the side of the receiver. The serial number should have an L in it and make sure the bolt matches (no scrubbing) unless the price is fabulous.
Check for LB markings which may look more like capital B's ....
Look for C Broad Arrow markings on the wood ....
Post pics once you get her home and we'll be able to tell you more...
Good luck ...
Regards,
Badger