Richhair, welcome to the forum. According to the Standard Catalog Of Smith&wesson, your model 36 was shioped in the 1973-74 time period(most likely 1973.) Your revolver is a 3-screw. The 3rd screw will be under the right side stock and your revolver has the square grip which is seen a bit less often than the round butt version. Many shooters feel that the square butt gives a better grip, especially for those with larger hands although the round butt conceals a slight bit better. The factory letter will tell you when your gun was shipped, with which features and who it was originally shipped to, usually a wholesale distributor or LE agency. You don't get much additional information unless the gun has a unique provenance.
I have a m36 round butt which shipped in 1974 and have carried it off-duty and as a backup since it was new. They are really nice little revolvers and I wouldn't part with mine. You probably won't either.
Hope this helps.