When Ithaca brought out the Model 66, darn near all prime time TV was Westerns. Maverick, Rawhide, Gunsmoke, Bonanza, etc. The lever design was to cash in on the Western cachet.
This was one of the better utility grade shotguns. Current 2 3/4 and 3" ammo will work, though the 3" stuff in that light a gun will make you wince.
One variant had open sights for slug use. Betcha yours is one of these.