Yes Ray, these are the can markings taken from the lid where they are a raised stamp and read exactly as follows.
(left, older, can)
20MM AMM BOX MK-3 MOD-3 RSMCO
INSP (Naval anchor) NORD 14267 OR 982437A
(right, newer, can)
20MM AMM BOX MK-3 MOD-3 U.P.C.
NORD 12468 INSP F.C.B. OR 982437A
Obviously, because of the Mod #, mine are much later than WWII. From personal experience I know ammo cans such as these were often reused for ammunition and other reasons too. Being watertight, they were popular as tool and storage boxes, on the ship and at the humble dwelling of the one who was able to slip it ashore on a dark duty night!