wow...that's an oldie...
Ithaca bought out Lefever in 1916. In 1927 they intorduced the Lefever Single Barrel Long Range field and Trap model.
That's a keeper for sure....congrats...
**edit.
also, I don't know if this will be useful to you, or if you already know all about the gun, but...scroll down 3/4's, and you'll see the Lefever name. It'll tell you what year it is....
http://www.doublegunshop.com/dgsnos3.htm
Lefever Single Barrel Guns - (Made by Ithaca Gun Co.)
Cheers.