Marlin would have used 400 grit on the frame, and maybe stopped off on 220 grit for the barrel, but it's according to how old it is, and the manufacturing process.
400 grit is almost a mirror finish, and with 220, you can still see the cut lines in the work that the grit leaves, similar to where a fine brush would have been ran across something.
On the frame sides, on the finish polishing, the lines with the 400 grit generally run front to rear on the frame, not from top to bottom. It's best to use a magnifying glass to inspect the steel, as it can tell you the direction of the final polishing wheel cuts or lines on the metal, if you can't see them clearly.
On screws and pins, you can finish those with 220 grit by rotating the ends and screw heads as you polish them. Some of these were actually rougher than that from the factory.
Finally, and the most important, keep all the edges sharp, just like the factory, as that will stick out like a sore thumb, even worse than screw holes. However, case hardening doesn't stick out as bad as bluing either.