I'd like to have some precision about the word "dashboard" in chapter IV of The Great Gatsby. According to Nabokov, Fitzgerald wrote wrongly 'dashboard" for "running board." But J. Bruccoli, who edited The Great Gatsby for the Cambridge Edition of the Works of F. Scott Fitzgerald, commented: "it is possible to perch on the dashboard of an open car. Emendation to running board is unnecessary and incorrect." I think he is right, but I'd like to know if for you "dashboard" means "the part of a car in front of the driver that has instruments and controls in it" (Oxford Advanced Learner's Dictionary) or something else.
He was balancing himself on the dashboard of his car with that resourcefulness of movement that is so peculiarly American—that comes, I suppose, with the absence of lifting work or rigid sitting in youth and, even more, with the formless grace of our nervous, sporadic games.
For me the word "dashboard" definitely means
"the part of a car in front of the driver that has instruments and controls in it."
In some of the old roadsters there could have been quite a large space between the dashboard and the front windshield. When Fitzgerald says "he was balancing himself," I don't picture Gatsby as standing on his dashboard but turning around and sitting on it with his feet resting on the front seat. If he had been standing on the running board, it wouldn't have been necessary to say that he was balancing himself with any extraordinary dexterity. People used to stand on running boards and ride on running boards of old cars all the time without looking particularly graceful. I have done it myself.
Nick describes Gatsby's roadster in detail:
I'd seen it. Everybody had seen it. It was a rich cream color, bright with nickel, swollen here and there in its monstrous length with triumphant hat-boxes and supper-boxes and tool-boxes, and terraced with a labyrinth of wind-shields that mirrored a dozen suns. Sitting down behind many layers of glass in a sort of green leather conservatory, we started to town.
So it is a very spacious car, and there are several windshields. It seems to me that there could have been a space of at least a foot between the front of the dashboard and the front windshield and that Gatsby could have used that space as a seat, since it was a roadster and the top was open. He might have wanted to do it because the interior was so spacious and so deep that it was easier to see out of it if he elevated himself.
I would be tempted to agree with Nabokov (whose opinion I had never heard of before) that Gatsby would be more likely to be standing on the running board if Nick had not commented that what Gatsby was doing required "resourcefulness of movement." It doesn't take any resourcefulness of movement to stand on a running board. It doesn't require any special grace or skill or daring. Therefore, it seems unlikely that Nick would have commented on Gatsby's position unless it had been somewhat unusual.
In fact, the reader might have gotten the impression that Gatsby was sitting on a running board, as a lot of people used to do in the days when cars had running boards. That would have required no physical dexterity or resourcefulness at all.
The old cars all had running boards on both sides, and if Nick had meant that Gatsby was sitting on one of them he might have said, "He was balancing himself on a dashboard of his car." Since he says, "the dashboard" it does sound to me as if there was only one dashboard and that was "the part of a car in front of the driver that has instruments and controls in it."
Since it would not be impossible to sit on a dashboard of an old-time convertible if the windshield was far enough away, I would be inclined to go with the original word and the interpretation you quote from J. Bruccoli. A dashboard has always been a dashboard, and a running board has always been a running board. I can't see F. Scott Fitzgerald making such a mistake.