This is an old thread, so I'm not sure if anyone is still paying attention, but I am Rubin's grandson. I "drove" this car when I was 8 or 9 years old...steering as my dad, grandfather and uncle pushed the car across the yard in Farmington, MI (where Rubin lived before moving to Southfield).
Rubin made all of the above claims though he never said "LeMans", he said "the most famous race in the world" but could never remember which race.
He was known as rather eccentric and had many tall tales on a wide variety of topics (he claimed he once drove a souped up Model T at over 100 mph), but I eventually did do some research on the Adler and much of what he claimed turned out to be true. It did run at LeMans as reported above, but it actually ran better at Nurburgring. There it was considered the fastest car on the track, but the plexiglass windows (!) kept fogging up and they had to pit several times to try and fix that. It still placed well. My understanding is at that time - in the late 30's - Nurburgring was actually a bigger deal than LeMans.
The car had a wooden floor, plexiglass windows, a tubular steel frame and an aluminum plate body. According to one source I found, the V-6 engine was hand built by Ferdinand Porsche, who gave it three carberators - one for each pair of cylinders. I wish to heck I still had that documentation, but its been lost in my 5 moves since I did this research (I lived in Washington DC at the time and did this research at the Library of Congress).
There were two cars, and I am unclear as to which ran in which race but they looked slightly different. The one above is NOT my grandfather's car. I know this because of the large Jaguar-style oval grill that runs vertically across the front. Rubin's car had a smaller oval grill that ran horizontally across the front.
We were always suspect of the Hitler connection, but we do know he bought it from a US Serviceman after WW II. Rubin's story was that this soldier was from the first US unit to get to Hitler's mountain compound (if you ever saw the last episode of "Band of Brothers", that's the place) and, finding it there, arranged to ship it back to the states. It is plausible.
As far as the connection to the '63 Corvette goes, other members of the family, including my father, remember him taking it to GM in 1960 or 1961. They said they had seen a GM brochure that included pictures of the Adler, but I never saw it. Rubin was a hoarder, and it no doubt decomposed with the other junk in his house. But I absolutely believe that this car was the inspiration for that split-window design.
I did my research in the late 80's with the aim of restoring the car, which was falling apart in Rubin's backyard. I had several conversations with a top-notch auto restoration outfit in White Post, VA as well as others involved in antique auto collections. I suspect one of these folks tipped off Jim, quoted above, that I was putting together this plan because my grandfather sold the car -- which had been rotting in the weeds for over 25 years -- for $50k the week before I asked him if I could have it. C'est la vie.