Unfortunately, Ithaca Gun, has also gone the way of the passenger pigeon, closing their doors permanently earlier this year. They used to have a good website, that showed all Ithaca 37's produced each year by the company, serial number wise. Unfortunately, I never copied this file from their website, never thinking they would ever go out of business. Here is what I know, as an Ithaca 37 was my first real gun purchased used, way back in 1967 or so(getting old, don't remember now). The designation '37' stands for the year 1937, the year they started business. My Ithaca 37 is a 12 gauge(I still have it), serial number 864,XXX, and was manufactured in 1963. This will at least give you a rough idea. Also, if the gun is UNDER serial number 855,000 barrels are NOT interchangeable, the gun was required to go back to the factory for a barrel to be fitted. Hope this helps a little.
Sincerely,
Garry