Damn I boiled the action with the stock on before I read the bottom line .....joking ..You have a few options.
Traditionally the furniture (that’s the trigger guard, top lever and forend iron) would be blued and the action lightly case hardened.
If there are any remnants of these original finishes it’s nice to leave them be and not go overboard with the cleaning / polishing.
Boiling on a stove with some soda powder will bring everything up nicely.
If all the original finish is gone then you can go for a shiny finish. A light going over with Autosol will do the trick.
Top tip: if you want the engraving / lettering to really stand out, give it a little hit with a can of black spray paint, then quickly wipe it off with a damp cloth before it dries.
The paint will get down into the engraving and make it really stand out.
It obviously goes without saying that you only want to be doing any of this with the metalwork off the wood.
I`ve not heard of boiling metalwork with soda (Bicarbonate of soda ?) , will definitely try that and get busy with some autosol , I guess it will be fun getting the screws out without fcuking them.