Feltwad- have you any idea why the barrels would be stamped 14, when they are a large 20? Lined? I don't think so. It wouldn't make sense to line a .693" bore with a .033" walled liner, that totals .068" difference - bit more if it was bored out a bit first. Considering this gun predates most all choke boring in England - who knows?
On the other hand, Taylor's Manton is stamped 15, which it is.