The subject of the Chaparral sucker car came up in the Smokey Yunick thread and I did some reading to inform myself. The subject in question was how much did Chevy R & D have to do with its design and construction. I looked first in a lovely book I have titled Chaparral and did not find much detail about that.

I have another book called Can-Am photo history by Pete Lyons. It has an extensive chapter about the Hall efforts. In it there is an extensive interview with Jim Hall. In it he says this about the 2j car, as the sucker was called.

He says it was other folk's idea to begin with. He actually states that he got a sketch from a kid describing a sucker car before any racing people spoke of the idea. People at GM R&D were interested in it and tried to interest Hall in it but as he says "I just did not have time to mess with it. We were building the 2H at the time and it turned into a handful, so the guys at Chevy went ahead and built the J car- which it was not called then, it was just another GM test car originally.
When the H car was so unsuccessful, we really had egg on our face. I got some vibes from Chevrolet, well why don't you take the vacuum car and run it? But it's scary when you stop and think how complicated it is. Its got a system of articulated skirts and it takes guys looking after that. And it's got an auxiliary engine that turns the fans, plus its a race car in addition to that...compared to cars we were running took about twice the number of people to just go out and test. ...taking it to a race track would be a real scene.
But they said this is a really original idea and somebody's gonna do it if we don't. Eventually I said "ship it down here and we'll see what we can do with it". They did and we tested it a lot and tried to make it into something. We eventually committed to run it in 1970 but it really wasn't ready to go racing. It was still a test car. We needed another year
." And the interview goes on to say it got banned and on to other cars....