Agree with Bob that this style of hinge would be possible on such a late built car as yours - looking at other San Jose examples but not on earlier built cars.
If your having someone else do the plating make sure that they do not use a high heat on the hinge springs. This can make them brittle when using mag or zinc.
In my experience magnesium phosphate produces a slightly darker final finish when compared to zinc phosphate and have seen both used successfully on judged cars. Don't recall a DYI kit for the magnesium but they may be out there
Thanks Jeff. I do all of my own phosphating in house. I use 190 degrees Fahrenheit approx, which I do not consider to be high heat. I was curious which color phosphate the factory used for my car. I have even seen hinges done in zinc and springs in manganese. I am not aware of any parts on my car that would have received a zinc phosphate only manganese. If that is not correct please let me know. The problem is when you see restored cars is that you don't have any reference point for why the owner did what he did. For some it is personal preference or perhaps they are mis informed as to what would be correct on their car, even on some high end cars.
Case in point here is a high end car that I saw at MCACN with zinc phosphated parts. Not sure why as I did not see the owner to ask him, but people were very excited about the car like it was done to a very standard. Any input would be greatly appreciated. Not sure what plant it was assembled at but assuming not San Jose. Was there a difference between plants when it came to phophating and was there a difference between 1967-68.
Thanks