I'm surely no expert but I THINK 400 grit may be a little TOO aggressive,unless the cylinder has visible matching marks.If it only needs polishing I think I would start with something finer....,maybe crocus cloth.You can always go coarser if need be.
The extractor can be nicely chamfered with a 1/2" diameter stone in a drill....
go easy,it doesn't take much.
Good luck!