Try cleaning the barrels with a stainless steel kitchen scrubbing pad and any light oil (3-in-1, CLP, etc.). The stainless pads do a nice job without abrading any remaining finish. If the cleaned barrels still need more attention, the quick way to refurb them would be a thorough degreasing, and then treatment with a cold blue such as Oxpho Blue from Brownell's. With some patience, you should be able to blend the bluing over the length of the barrels. It won't look like fresh rust bluing, but it should look OK for the gun as you have described it. If you do a search on this site, you may find some detailed instructions that were posted a few years ago.
