Dan - I guess I wasn't aware that you were placing some auto racing in the Gallery. Saw you just finished the Canadian Indianapolis Speedway Winners.
Here are a couple more somewhat obscure sets:
(1) 1954 Stark & Wetzel 500 Mile Race Winners. This is a 37 card set printed in 1954 with cards for each of the race winners through 1953. Note there were no races in the years of WWI and WWII. Cards are rectangular 95mm x 66mm and were originally cut with a serrated cutter. The cards were used as backing cards for bacon. Thus the cards are blank-backed, and wax-coated. Most cards will have bacon residue on the back side. A friend who collected these when they were printed stated his Mother tossed his first collection due to the smell. He hid his subsequent collections. This issue probably contributed to the scarcity of these cards.
(2) 1961 Marhoefer Indianapolis 500 Drivers. This is a 10 card set that is the first of 8 Marhoefer sets featuring drivers and cars from the Indianapolis 500. An earlier Marhoefer set featured airplanes and missles. In this set, the cards are rectangular with sharp corners, as opposed to later Marhoefer sets with larger cards and rounded corners. These cards measure 100mm x 84mm. The cards were used as backing cards for Marhoefer weiners (The Weiner thats a Winner); and, like the S & W set above were wax-coated and often show meat stains (and the associated smell). Unlike the S & W's, Marhoefer placed driver bio information on the backs of the cards. The 8 racing Marhoefers sets were 5 different drivers sets (1961-1965) and 3 different "Review of Famous Racing Cars" (not certain on dates, but believe 1962-1964). The "Review" cards were not in weiner packs, rather in packs of "Sparkies". The "Review" sets featured 10 cards per set. The driver sets varied in the number of cards each year.
Both of these sets were issued locally (Muncie, Ind) I believe, and are a wee bit difficult to complete. The S & W set has at least 4 cards that are very difficult. Since the universe of cards is so small, I do not know if these four were short-printed, or the supply was effected by collectors/hoarders.