Welcome to the wonderful world of British doubles!
Those are still British proof marks. The crown with the R is a reproof mark and when it was reproofed, it measured as a 12 gauge with 70mm (2 3/4") chambers.
The 14/1 indicates that one bore measured (9" from the breech) between .701" - .709" when it was originally proofed.
The 13 indicates that the other bore measured (again, 9" from the breech) between .710" - .718" when it was originally proofed.
From this info, you can determine how much material has been removed from the barrels if you are able to measure the internal barrel diameters. This will not tell you what the wall thickness is, which is the most important piece of information. Pictures would help a lot. There should be more marks indicating what the bores measured at the time of reproof and they will be metric.
