These were firefighting SCBA's (singles) in an earlier life, ca. 1960's. I acquired several from a fire department a few years ago, and finally go around to putting two together in a somewhat unusual configuration (compared to today's norm).
Shown beside 38's for size comparison, they are virtually the same length, but only about 5.25" in diameter, maybe slightly more. Weight as shown and full of air, 28#. I think these will be fun to dive with.
The thing I like about valves down is the ability to keep track of approximate remaining pressure without a pressure gauge by using the "cascade" method. If beginning with 2200 psi, and only open the starboard tank valve, I can breathe that tank down to point of increasing breathing effort, then open the port valve to let them equalize. They would each then have a little over 1100 psi each. Closing port valve and repeating the procedure will result in each tank having over 550 psi. Depending upon depth and other conditions I can begin ascent at that point or once again turn off the port valve, saving that half of the air supply for ascent when the starboard side gets low. Perfect for the easy diving that I will use these for.