The correct color was referred to as Dark Grey. According to Paul Herd's "Chevelle SS Restoration Guide", the codes were (by manufacturer):
DQE-32961 (Ditzler)
71B16 (Rinshed Mason)
9901L (DuPont).
However, my paint supplier (PPG) advises that the foregoing numbers are not currently valid. He was able to cross-reference the number as DCC32961, in PPG.
This paint is extremely low solids (very watery). It will require at least three light coats to cover a properly primered wheel. Avoid the temptation to put it on wet. When it dries, it has very low luster. The correct appearance will look like an old magnesium wheel.