Naval jelly was for a Brown gun with no original finish and not to be fully restored. Like the one the thread was started about.
Mark, as I understood the original post, the current brown finish is likely the original finish which has oxidized and slowly converted to a different form of iron oxide. SKB mentioned the possibility of reconverting that brown rust (ferric oxide) back to black rust (ferro-ferric oxide) by boiling and then carding after cleaning. I feel this is probably a very good way to go so long as the brown patina is even, and perfectly clean.
al didn't mention if his G grade Lefever has fluid or Damascus steel barrels. There is a very good possibility they are Damascus since Lefever ended production about the time that fluid steel was overtaking Damascus in popularity. If his barrels are Damascus, he may wish to take further steps to clean or etch to bring back the contrast in the pattern welded tubes.
I don't think I'd want to boil the action, sideplates, or forend iron. After cleaning with the ultrasonic cleaner or otherwise, often a light cleaning with oiled 0000 steel wool will remove light surface rust and reveal what may be left of the original case hardening colors. Abrasives like emery cloth or scotchbrite pads will scratch and remove any remaining case colors, but they will withstand light cleaning with the oiled steel wool so long as you don't get too heavy handed and make sure to use nothing coarser than 0000. Even faded or mottled case colors look better and more original on a vintage double than the high polish (or worse--- cold bluing) some people do. A good cleaning like this can do wonders for a dirty and neglected gun without resorting to complete refinishing.
