Surface grinding experiment with Shopsmith

[ductape]

With some care and the use of a fairly good grinding wheel, there's no reason why this wouldn't work for the intended use of the plate.
The process itself provides a spark test to determine the metal. Cast iron will make short, dark red sparks. Mild steel will make longer, yellow/white sparks. Another way to tell is to rub a sheet of white paper over the freshly ground area. Cast iron will leave graphite smudges on the paper. Steel will generally not.