Thanks for the photo, they do look similar. When I was 16 I bought a pair of aluminum 90's off a lifeguard who said he used to be in the Teams. The tanks were black, even had UDT frog decals. They weren't available to civilians as you say. Everyone, including myself up to this point were stuck with steel 72's. Being fairly small and good on air, imagine going from 72 cft to 180 cft. in a day?! It was like discovering a new technology. They were made by Northhill out of a solid block of aluminum on a lathe. Do your tanks have a round circle in the bottom? If so, those are the bases of the fluted plugs they patched the lathe attachment hole with. One of mine started leaking while being filled in the Keys. Expanding air bubbles coming out of the base of the tank. About gave the dive shop guy a coronary. I ditched the tanks shortly after.
A closing note on the lifeguard. A nice guy and into hang gliding with the old billow wing gliders. The kind without wing battens, hadn't been invented yet for the open market. He was doing a demonstration static drop from a balloon in 1974. He was released from 5000 ft. but in nose downward in a stall. The old gliders when they entered a stall stayed that way I understand, lacking battens to maintain a foil section. He didn't survive the flight tragically.
