You can obtain a historical letter from S&W
What model?
Impossible to answer without more information.
The Standard Catalog of Smith and Wesson, 3rd Edition by Supica and Nahas will give you plenty of information.
Smith and Wesson Model No. 2
Standard Catalog of Smith and Wesson, 3rd, edition
If you contact Smith & Wesson, they will give you that information.
More information needed.
No way to answer without more information.
The Standard Catalog of Smith and Wesson, 3rd edition, by Supica and Nahas.
Impossible to answer with the information given.
1950-1969 for exact information, it is worth the price to get a factory letter from Smith & Wesson
The frame size of a Smith and Wesson model 66 is K.