Sweet! Thanks everyone for your help and input do far. I calculated the measurements of the tank and turns out to be a 500 gallon tank. The guy I bought it from never used it so he was not sure on the capacity. After thinking about the grill portion of the smoker I think I will use 3/4 of the tank for a smoker and then block off only a 1/4 of the tank for a grill. Like some have said, it's just for the ability of throwing on some burgers while smoking throughout the day.
That is what I like about nthis site!!!! My wheels are turning in my head thinking the 2 in one build is something I would want to do, whether charcoal or gas not sure.... But is is "on like chicken bones now" !!!!!!
I have a 250 gallon propane tank pit that I built when I was in high school that Im thinking about standing up vertically on the end and use that as a firebox and top side as a warm box... I'll post a pic of it in a minute to see if we can come up with something here