I think you are Toby from Suffolk, right, and you own Barclay's Bank, is that correct, chuckle.
Very sorry to hear about your amputation, old mate.
Anyway I have a Lang just as you describe I bought at a rural Canadian gun show for $300 bucks. It needs new barrels or sleeving, right now I am scouring Canada for a stout pair of Damascus barrels to be parted and sleeved onto the Lang breech end. I have an English gunsmith who immigrated to Canada who is prepared to do the job if I can find suitable donor barrels, rather than sleeving with new steel barrels.
Are you out Lavenham way, or is it Melford?
Mike, from Coggeshall
Have you pulled out the lock and looked the the mainsprings> They are curved, and the whole lockwork is exquisite