These guns should be parkerized but I have heard cerakote is suitable as it’s very thin. I have used Duracoat with an airbrush on the exterior components but not on any moving parts. The originals were done in zinc or manganese phosphate. SWD was particularly proud of their finishes and sold their “famous” bluing salts and phosphate solution out of their catalog. The SWD guns used a pre-black dip prior to the park job, makes it much darker like a black color instead of gray. I personally love those dark black SWD m10s, like the Texas guns.
As for the bolt, it can indeed be “fixed” with a grinding implement or even a hand file. The peened sear engagement surface just has to be reshaped. you can also weld up the beat down notch and recut it, it works as a temporary solution until a suitable replacement can be secured, but this is not recommended when a brand new one can be easily obtained off the internet.. more of a “SHTF” kinda fix.