You've got a good memory, Eric. That was in 1973. Jim Gronen of Boulder, CO was assisted by his Uncle, Robert Lange of the Lange Ski Equipment Company, and they came up with the idea and the device.
I raced Soap Box Derby in 1974/75/76 in Orange County, CA and came in runner up in the 1976 race. Almost, but not quite made it to Akron, Ohio for the finals. (I still have my car from 1976. Not sure what to do with it). That was as close as I ever got to "big-time" auto racing. I have read that Dale Armstrong also raced in the Soap Box Derby as a young teen.