Mark, plating is done to the carburetor small parts, most are steel, a few are brass on some models. The plating process used on the steel parts is to add a tin/zinc coating a few mil thick via the eletroplating process. It's not all that complicated, or difficult, but does require good surface preparation, and close attention to detail for best results. One must keep in mind that the smoother the base material, the brighter the finish will be on the final product. The plater has the option to add yellow chromate to the plated parts for a "gold" finish.
The main casting and airhorn, along with some of the choke housings are an alloy. I'm not sure of the exact "recipe", but they are prepared with a zinc/chromating process, not electroplating. I will say that the basic "recipe" is not the same over the years, because the results we see from the zinc/chromating is not consistant thru the years of production. My guess is that early models have more lead in the material, because they tend to come out a deeper/darker color than the later units.
I have talked to a few "builders" who are experimenting with plating the castings inside and out for E-85 testing, but haven't heard anything more about if, when, and how well it's working?
The baseplate will NOT react with the zinc/chromate process, they are probably a cast aluminum material.
Another option for the main casting is to use Eastwood spray paint. LOTS of builders do this, it actually looks pretty decent if the castings are completely stripped down first. Seems to hold up OK. We do NOT do it here, we use real zinc/chromate instead, and paint will NOT protect the internals from contact with fuel, fuel additives, ethanol, alcohol, or water........Cliff