I was cleaning under my 55g today and found a sticker saying 72 bowfront stand. What an excellent surprise! Here it is about 90% complete. The decor and fish are all finished I just need to fix the tubing fiasco so that the bubbles come out of both rocks again aswell as the bubbletube across the back.
So there's where my missing gallons went... I bought a "55 gallon" bowfront off Craigslist recently and it measures out at about 40 gallons without substrate. Oh well, it's a nice tank and I got it cheap enough.