Joe Freeman of Boston, MA, drove this very attractive car to an 8th place finish.  Since I know nothing of the "Sparks-Thorne Little 6's" history I would be very grateful if anyone would like to contribute some information.

David W. Braun contributed this info on the car:

See Mark Dees' Miller Book, Eliot White's Offenhauser book, and Borgeson's Twin-Cam book.  A sister car was the 1946 Indianapolis 500 Winner. 

"Interesting aspect: asymmetrical inclination of the valves (the valve included angle does not correspond with the vertical centerline of the bores).  Idea here was downhill flow of the incoming charge, rather than the straight-through of a cross-flow head. If you squint just right at the Sparks-Thorne engine, the intake cam cover is noticeably higher in elevation than the exhaust cam cover!!

The only other two pre-War engines that I am personally aware of which used this design feature was the 1922 Sunbeam GP and a one-off 1936 Harley-Davidson racing motor.