Bravo Nick - I had forgotten about that publication. I also was a Boys Life subscriber for many years, and well into my late teens. I recall that the Opel Kadet was used as a "mule" for many experimental engines; including the Wankel IIRC.
I wonder what ever happened to that Sterling engine concept; seemed like a great idea.
Yea, Boy's Life was full of things young boys would be interested in. I will post in another topic some of the bicycle advertisement of the day which included Raleigh, Schwinn, Huffy, Fuji, Sears and Murray with Bendix offering a stick-shift.
Regarding the GM project, I suspect the battery technology significantly lagged the engine capability and shelved the project.