Bringing back a thread to life, Your J.C. Higgins model 66 is a shotgun produced by High Standard for Sears. It is the ""Off Brand" Equivalent to a High Standard C100, or C1200. I have a model 66, 583.603, and I'll put it side by side with any Remington 1100, any day. Largest problem with these shotguns, is some parts are now made of pure unobtanium (lol) due to having not been manufactured for 30 some odd years now.
Check here. John Stimson is pretty much "The Authority" on High Standard/Higgins Shotguns.