Fuel Tank Size

[bobfish21]

Not sure if I'm in the right category here. Coming home from a late night fishing trip on my '74 23 Tsunami, 260 efi/ alpha 1 I/O, ran out of fuel 100yds from my slip. Put 10 gal. in to get me to the fuel dock, filled tank and it only took 43 gal. Was under the impression I had a 72 gal. tank, but the numbers tell me more like 55. Boat has the fishbox/ livewell setup immediately aft of the fuel tank, which is original but in good shape. Can Anyone with any experience with this model tell me what size tank is in the boat? Concerned that maybe I have fuel pickup issues. Also, if I opt to install more fuel capacity in the near future, is there room for a larger tank, or will i have to add a second aux. one? Thanks for any advise!