Is American mystery racer an SWM prototype?

Now, last week I bumped into some old pictures of a racing prototype built under the SWM name in Germany in the mid-1960s. This car was sold through auctioneer Bonhams (here), which gave some interesting information in its description. It was supposedly made in small numbers (6 to 7) by brothers Stefan and Wenzel Mannl of München. The cars originally used BMW 700 boxer-power 'which was later changed for an 850cc unit equipped with twin-plug ignition'. They were hill climbed and raced at a great number of events, amongst them the Ratisbona Bergrennen, Sudelfeld Bergrennen, Neubiberg Flugplatzrennen, the Schainsland hill climb, Rossfeld hill climb (where no less than 3 SWMs were entered in 1965) and at the circuits of Trier, Ulm-Laupheim and Innsbruck.

What struck me most is the body shapes and the size of the SWM prototype, definitely bearing similarities to our American mystery racer. At least more than any other contemporary racer car I can think of. Owner Steve Steeb ads: "Interesting. Similar wheel openings and front and rear profiles. I'll go back down the rabbit hole and see what I can turn up. I also recently contacted a guy in Florida who does a lot of research on American fibre-glass one-offs. I sent him a few pictures. He apparently travels sometimes and I am close enough to Detroit that maybe he could come see it someday. Meanwhile it is tarped and awaiting its turn in line (might be a few years!). THANKS for keeping me in mind! Cheers, Steve". Do let me know what you think, too.