I had an online conversation just now:
Charles Merrill:
"not a kit car, a pure original design by Jo Karezek, with a 383 Chrysler wedge head. With a unique Karezek design gearbox. I promise as I have actually had my hands on the car in 69, in Vienna where the photo was taken. "
"Nothing whatever to do with McNamara, as McNamara did not build cars until 1968, and I joined McNamara in August 1968, and started building around chassis no. 8 of the Mk1 Sebring Formula Vee cars which is the class of cars that McNamara started with."
Mr. Merrill indicates the vehicle was called the "KaKa". Articles also refer to it as Kar-Car.
Karasek and Karezek are frequently used for the same name.
Articles indicate the car had a 6.4 litre engine. 389 or 390 cubic inches is not a normal size for either a Hemi or a Chevy engine. Taking a Chrysler 383 Wedge to 6.4 litres wouldn't be difficult.