Sorry, I should have asked what car number we are talking about here...I had later '66 cars on the brain.
As mentioned, the bolts for the Koni shocks are totally different. I can't say for sure, but I think those particular bolts may have been cadmium plated as Jeff mentioned, rather than clear zinc. That may be a difficult one to nail down though.
I do not believe they were ever zinc dichromate (gold.)