If you are trying to get the gloss back in the brass, you can use a buffing wheel on a bench grinder along with jeweller's rouge. These are both available at Princess auto. The data plate on the front can be de-soldered before the buffing takes place.
I have several of the DND ARMY marked extinguishers in about 3 or 4 variations of markings, and have had to play mix and match with civilian versions of the same extinguishers in order to get good bodies(or to tap out some dents) onto the ARMY embossed tops, . I have also seen a few of these completely painted over in Khaki, so this could be done too, and you wouldn't have to really restore anything. Soldiers didn't really care much about data plates (cause they already know everything) and would not neccessarily take care not to paint over the plate either.
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