My 53 would have come in Champagne grey. I've been told the original colors have long been lost. Chevy duty's color is supposed to be a good match though or so I'm told.
I think it is a Sherwin williams product. Jim Carter has it as well, but in Lacquer. I'd like to do acrylic enamel instead, so I'm probably going with the Chevy Duty stuff. I just don't know if it is pre mixed to just "dump in and blow" or if additional additives are needed. I suppose a primer would also be needed.
I got a lead on a PPG color here some time ago, but someone else said it was a poor match. It was 3613 or something like that. It was a metalic grey. I almost had it made up, but backed off when the other guy said it didn't match.
I've talked to a couple different people about formulizing it in DCC, but I don't have a good sample to match.