It certainly CAN be restored, but that implies putting it back to as-new condition and that is not a do-it-yourself project. Professional restoration would probably cost more than the value of the restored arm. Actually a restored arm, no matter how skillfully done, is usually valued very little higher than a similar gun in NRA Good condition and a poor restoration much less. If all the parts are in the bag, a replacement buttplate shouldn't be too expensive, the rust can be stopped, a good furniture polish on the wood parts and gun oil on the metal, re-assemble it and you have a Good to Very Good shotgun. I'm not sure just which Ithica you have, but since you say Hammerless, I'm assuming that you the Hammerless Double and grade 1 would be the field grade according to my 1995 edition of the Standard Catalog. It lists a value of $650-$850 in Good and Very Good, so should be a bit higher now. Single trigger, vent rib, auto ejectors, and a beavertail forearm can each add $150-$200. Even if you pay a gunsmith for cleaning and assembly, you should come out ahead. The Catalog also has a caution that those made prior to 1925 should not be used with modern ammunition, but doesn't give a clue to identify those. Someone probably has a serial number list.