I was afraid that someone would ask that question--after all these years. Kurt knows something that I haven't heard of, which is good info.
I have a 1968 European car magazine that did a review of foglights, and they called it the Marchal 653/656, which I took to mean that the differences were slim.
I DO know that if you put a higher wattage bulb (OSRAM type) that these lights are waaay too bright. They were also a "stock item" on the street version of the GT-40 from Shelby in 1967. They sit just under the headlights. Perhaps that had something about Shelby spec'ing them for the '68 Shelby and GT/CS.
These lights (653?) were also used on the Ferrari Superamerica, and 350GTO. That's what ups their value. Don't park near a Ferrari that needs driving lights! LOL.
The State of California HATED these lights, and deemed them illegal in '68. There wasn't a review authority for things like fog/driving lights then, just an on-the-spot review by the CHP.
Thanks, Kurt, for the info, because there is very little info out there on the internet about these lights.
Paul N.