cleaning the case with paint stripper would leave a better finish for clear coating it.
then coat it with clear engine enamel.
giving it a light sandblasting or bead blasting would be an easy job, it leaves an even finish,
and is an excellent base to help the clear engine enamel stick to.
a wire wheel will mark the alloy, and it is very hard to make it look even.
and it also leaves a pitted type finish
second gear problems, could be the lever that's spring loaded and sits in the shift star
either the spring isn't returning properly, or it's stretched, or the notches in the star aren't deep enough.
it could be the shift drum or the shift forks are worn, was there much movement up and down when you fitted them together ?