Start with a dead-flat surface, like a surface plate or pane of glass, and some high-grit abrasive papers, at least 220. Disassemble everything, including to take the frog out. Run the sole over sandpaper on the flat surface to see if it’s flat; back down to lower grits if it’s really bad. Do the same with the machined surfaces of the frog.
Simple rust removal with a wire wheel, steel wool, naval jelly/Evapo-rust. The flat-sandpaper method is not ideal for removing rust from the lever cap and blade, because they’re flexible enough that pressure distribution can change the metal removal pattern.












There’s your problem. If you start with a false premise, all your subsequent logic is invalid.