Similar to the Pony Express Set, the Katy Flyer sets appear to be a small clockwork startup sets. The two examples that we know of were stamped Outfit No. 2 on the side and appear to be from 1927.  Outfit No. 2 was a slightly more expensive set than the 'Ought' set that came with the Pony Express. The picture below shows the contents of the set except for the No. 5 clockwork.