Hi Steve, I,ll try to answer your queries in order......Masu Brothers at 3a Wigmore street. London proof. Yes, you are right, the fore-end is fixed to the action.
I will try to post some details of an interesting Masu Bros pinfire that I owned, and which was sadly stolen, ( a long story).

Yes, the Blanch did have the stud on the action flats. There was no indication as to who did any work on the gun. The serial number on the Blanch with the grip msafety was 3626. The only number that could be found on the other Blanch was the number 307 on the fore-end hook. Clearly, not a serial number. The silver disc on the stock had a now-defunct coat 0f arms, believed to be Marquis of Hertford, but not 100% sure of that.

More later. Dave