Look at the grip screw escutcheon. It's brass. The evidence of plating is the finish itself.
Notice the difference in color and sheen from your frame? My bet is the frame is gold plated. Whether original or aftermarket, I can't tell. A brass frame-no matter how well kept, could not possibly be that shiny after that many years. Even if it were polished recently the difference in color between brass and gold is obvious.
I agree there is no visible evidence the Sharps was ever plated.