According to Sandy Petersen:
Steve is an old friend of mine, and he did in fact help germinate the American Gothic idea (the name was his idea, for instance). Another pal of mine, Marc Hutchison, was involved from the start. Steve wrote up a treatment basing it largely on D&D...The PDF document, which you can download here, is short but fascinating, particularly since it was written in May 1977 and uses OD&D/Chainmail terminology in places (such as the fighting capability of the "Mycenean Thought Crafters" class). Reading through it, you can see a number of things that call to mind the lost version of psionics that Steve Marsh created that was later reworked for inclusion into Eldritch Wizardry. It's well worth taking a look at this if you have any interest in the development of the games and ideas of the hobby.