If you try to strip off the new paint it could wind up looking like this (photo #1 & #2) any way. So why not strip it down to bare metal and repaint. It will look brand new. I strip everything down, prime with an automotive etching primer, spray paint the finish coat and bake 30 minutes at 200 degrees.
They look great and wear well.
PS the diner was made from a Lionel #610 junk car.