That looks to be a round over plane (pre router tool) and the blade would have an inside radius curve to t/I'd bet the blade would have to be ground from raw blade stock, as I doubt they are available.
I'd stick with WD-40 for cleanup on the painted surfaces, and either paper towel or a soft tooth brush for te tough grunge. Leave the paint alone it's mostly intact and any attempt to repaint would wipe a lot of it's value (Sorry no clue on that, while i casually collect then when they pop up, I'm not a die hard collector)
The metal surfaces you can go at with fine steel wool and oil or more WD. Keep the Steel wool off the paint though...
Nice interesting little piece, I would mind finding one like that.