Gary, That document shows a picture of a Grand Prix stereo, for sure the 1970 and older had a mono Grand Prix.
JB, 516 is the code for the European Grand Prix. 519 is the Grand Prix for the USA. I only state that so that we don't confuse people.
There is no "531" on your data card? Yours is a 230 SL, so maybe that plays a role, but of the data plates and data cards that I have looked at, all that had 519 also had 531. But, clearly they were separate options.