No.4 Manufacture Date Inquirery
Have a look at Ian Skinnerton's book, "The Lee Enfiled Story". It should be of great help to you.
The book covers everything about the Lee Enfield Family of Rifles. It even gives you the production figures per month from Long Branch, Savage, BSA, etc.
It helped me with the research on my BSA-Shirley No.4Mk1, which was FTR'd in 1949 at Fazackerley ... /49 (F) RTR.
Have a look at this book. It should help you out a lot.
Also have a look at the left-hand side of you butt stock ring. There should be some stamp markings there. These should give you some information on when, who, where and what serial number the manufacture gave your rifle. If your bolt is original to your rifle, the matching serial number will be located on the aft-face of the bolt arm; as it was with mine. This is standard practice.
Best of luck to you. Let us know what you find out.
Rgs...kajn65 (Keyan)