I don't own one, but I hate starting a thread posting and no one responds. So, I am going to make a educated guess. I own a 24"x48" custom built offset smoker. I would guess about 4 ~15lb brisket packers, or 8 whole chickens, or 8 butts. It may depend if the pit has a heat deflector out of the firebox on how close you can get it. That could reduce the capacity down to 3, 6, 6.
These numbers are all on the bottom cooking grate, top would be half of these numbers or less.
I would suggest if the budget allows for it to go with the Kingsman or my choice would be the Stockton (lots of space). You can't get full aluminum pans across a 20" pipe barrel.