Pre WW2 American Flyer produced Wide Gauge and O gauge trains. The actual scale was the same as Lionel, in other words it varied a lot. In 1938 A.C. Gilbert purchased American Flyer from W.O. Coleman and moved production from Chicago to New Haven. The 1938 train line was carryover O gauge plus the addition of the new Gilbert HO trains. Wide Gauge trains were discontinued prior to 1938. In 1939 Gilbert introduced the first engines that were accurate 3/16 scale models that ran on O gauge trucks. By 1941 all the Gilbert O gauge engines were made to 3/16 scale dimensions. In 1946 Gilbert dropped all O gauge products and put S gauge trucks on the 3/16 scale models and introduced the 2 rail S gauge track.
The 1934 Zephyr has no relationship to postwar American Flyer products. While it is O gauge it is also made completely different than Lionel O gauge was at that time. My guess would be those who collect and operate 1938 and older American Flyer would be posting in the Tinplate subforum.