That number 680 was never issued by Lionel for any rolling stock, let alone a caboose. The 657 was the caboose issued in the 600 series cars. The number doesn't appear in 2-7/8" gauge, Standard, or 0 gauge, at all. Have no idea where you came up with that number????? Possible restamped by someone before.
Searched TCA Standard of the World, Doyle's Prewar Catalog, Dave McEntarfer Prewar Sets, Greenberg Guide to 2 -7/8", & Standard gauge, Greenberg Guide to 0 & 00 Vol. II, and NO 680 appears anywhere.