With regards to the flatop, my dad made it about 40 years ago. The cast top came from an old restaurant. It works great.
Not sure what the gallon capacity of the tank is, but it is 30"x72. The firebox is 28 1/2 wide, 24 1/2 tall and 20 1/2 deep. It's made out of 1/4 plate.
I really appreciate all the nice comments. Can't wait to to start cooking on it.