Thats the correct place for theobens and hand engraved was the norm back then. Cant help with a date as they didnt sell very well, The first ones we had in the shop came back and the buyers said they are very inaccurate with any pellets, They had not even tried Prometheus pellets, They thought it was a normal run of the mill Theoben. Why make a barrel to only shoot prometheus but i have seen them shoot other pellets just as well as other theoben rammers even if very pellet fussy. Plus Ben is still making weird barrels, Smooth twist and stx so he certainly knows what he is on about. I have the very first rifle he made and not even sure what barrel is on it. Will have to ask him.
Let us all know how it gets on as we have a better choice of pellets these days. Col