I just cleaned up a Kennedy box that I'd originally planned to restore... it was a lot rustier than your Proto and it turned out much nicer than I expected, so I'm planning to leave it as is for now.
I've had good luck going over it with steel wool and some PB Blaster or WD-40... then some simple green and a coat of wax.
If you do this and don't like it, it's easy to just clean and paint it.
