Not trying to start an argument, but one of the finishes used on carburetor hardware from the 1920's forward is white zinc.
White zinc with a yellow conversion coat was being used at least as early as 1939.
But to the OP's question: even when we were doing 500 + carbs per year, it was cheaper to have plating done by custom shops. And yes, I DID TRY one of the expensive "home" plating outfits.
Don't recall the brand, but it came out of southern California. We paid roughly $1500. for it about 1990. I was NEVER happy with the results, and sold it to a friend for experimentation.
Jon.
