I think that's a re-worked 3rd Model Bess imported and sold as a parts gun with a modern replacement stock, sold by IMI, that has been stamped to be something that it's not. There is no border around DUBLIN CASTLE, as well as was mentioned that the N in Dublin is reversed. Also the crown and arrow "acceptance" stamp appears to be beneath the large crown stamped on the lock plate, when it should've been applied after or "on top" of the crown. It's a real 3rd model Bess, but I don't think it was made in Ireland.
LD