1st, you need the serial number. That will help determine when it was made. Ithaca "models" are based on date.

You can look up the serial numbers here:
http://www.doublegunshop.com/dgsnos3.htm

The Grade is determined by the amount of engraving.

It should also be stamped on the gun. For instance this is a grade 3 Crass.







All 3 of these are Crass guns.



After you have the model, gauge and grade, it will depend on condition. I am sure others will be help. Walt Snyder, who posts here frequently, wrote a great book on Ithaca.

Pete

http://www.damascus-barrels.com/Movie.html