Part of the O-27 line, the 1668 (manufactured 1939-1941) typically headed sets with 1690/1 passenger cars or 1600-series freights, both of which came over from the Ives catalog and continued by Lionel for O-27.
I received this 1668 in a set (box marked 1174W) that included a single 1630 coach and a 1631 observation. According to Greenberg, the set should have included a 2689W tender, but the one in the box has no whistle. It also has a latch-style coupler, while the coach/observation cars have first generation box couplers. Even weirder, the coach has a silver roof and trim, while the observation has a gray roof and trim. Supposedly set 1174W was manufactured/sold for 1941, the last year the 1668 was produced. I've often heard stories of Lionel and Flyer emptying their warehouses to make sets to sell just before toy train manufacturing ended and war-time production began. Maybe this was one of those.
