Joe,
I am no magician...

I just spent a lot of paid time to study the subject, which makes me some kind of a semi-expert with still a lot to learn...

And I find new stuff every day!
No less than 4 NASCAR bodies showed up as accurate, 3-view line drawings in a 1967 Revell 4-page flyer. None were ever issued despite that molds were created. In the same catalog was a line drawing of a Lotus 38 Indy car body.
15 years ago, I was able to purchase some clear examples from a fellow in Bakersfield, then I ran across one of the Revell project engineers, then retired, and got this car and a ton of other prototype bodies, cars, chassis... and one of those Lotus bodies plus that of a Mirage-Olds, marked "sample" by the same hand.
And guess what, here it is, on top of that flyer and with a prototype chassis apparently designed for it: