Congratulations, sounds like you have a fine rifle. The first thing to do is find out what chamber you have and what is the diameter of the bore and grooves. I'm not sure if the early 500BPE 3" was a paper-patched bullet or not. All the American PP bullets were bore diameter. Once you (or your gunsmith) make a chamber cast it will be clear what case and bullet you need. I would hold off buying any components until you have the measurements.
You will also need to know the rate of twist to select the proper bullet.
