Identifying what plating was used on older radio chassis

[wrangler007]

I'm doing some restoration of 1960's vintage Heathkit amateur radio equipment. In many cases there are rust spots, and generally the chassis are dull. The chassis, upon which circuit boards and other components are steel, but I don't know what it was plated with.

I participate in a Heathkit Yahoo discussion group, but no one in the group knows the answer. I want to make sure that if I replate with Copy Cad, for example, I would not be causing a chemical reaction that makes the situation worse.

Is there a chemical test that i can perform to determine the original plating metal?

Thanks!