@ Arunas: I never heard of the Eagle Debonaire either, and normally I don't deal with relatively modern limited production, or non production models (early 20th century cars are a different animal in that many never achieved mass production). However, in this case, I made an exception after the Clenet marque was raised, but ruled out. Back in the late '60s and early '70s, I was fascinated by the various retro replicas which were very popular at the time. Marques like Excalibur, Corsair, Gazelle and Zimmer, as well as the aforementioned Clenet were very popular here in the US at that time, and I knew several people who owned them, although they were beyond my economic means.
With this in mind, and noting that the car was RHD and shown on the left side of a roadway, I made the usual assumption that the car was from the UK. But the UK (and Australia) were already ruled out as originators with the US established as the origin, but "modified elsewhere". So, I thought, perhaps the elsewhere is the UK. Because a frequent source of puzzle cars is from "For Sale" ads, I decided to spend a bit of time looking at exotic cars for sale in the UK, using a well known UK website for classic car ads (name provided via PM upon request). Luckily it didn't take too long to run across the Eagle Debonaire, which looked like the puzzle car, but the pictures provided were not the same (completely different background). However Googling "1965 Eagle Debonaire" quickly yielded the puzzle matching photographs from another ad magazine. This confirmed that the puzzle car was indeed a (the?) 1965 Eagle Debonaire.
All I know about the car is what is given in the advertising information, although I haven't spent a great deal of time attempting to gather information beyond that required for the puzzle solution (the already established Mustang chassis and Chevrolet V8 power). The information did say that the car was the idea of a wealthy American who had ideas of producing cars of this type, but it is implied that he never got beyond one car. Whether he built it himself, or commissioned it from an established company is not revealed in anything that I have seen.
Hopefully this answers your questions.