Ok, for here go nothing.. With you guys help I decided to go with the 80 gal tank.
I probably jumped the gun a little by cutting the door first. I couldn't stand, I had to cut something or else I wasn't going to sleep.
Here's were I'm at so far.
I got the door cut and the hinges on, and also cut off the legs and compressor mount.
I'm ready to cut the firebox opening.
Pit calculator says 54 sq in opening to cc. If I laid this out correctly I should come up 6" to make my horizontal cut on the tank, do that sound correct for a 24 diameter tank?