Awfully nice offer of Police to refinish your metal for you, but I sense you wanna make this a personal project, and with a gun of this grade and condition I couldn't agree more...you'll learn a lot and have a nice feeling of accomplishment for doing it. What you wanna do foremost is to get an evenly surfaced finish while doing as much as possible to keep the edges and contours sharp...use the "black" wet or dry paper, 320/400 grit....you dont want to "polish" the metal to a mirror finish.... on large surfaces like the sides of the upper receiver and the left side flat on the frame, use the paper on a sheet of glass, like out of a picture frame...for smaller flat areas, use a .040 or .050 feeler gage as a backing for the sandpaper...on curved surfaces, use 1/2 wide by 2 in long sections cupped around the first and second joint of your finger and just " roll" around the contours....look at pictures of known original guns to see which direction the "grain" (machining marks) of different parts go, and do your resurfacing in the same direction.
After a few or more hours and a six pack or so later, you'll have your metal prepped and ready for you to try rust bluing!!!
Read the stickys on here for that info.