I ran some numbers and here it is if your tank is 36" wide BY 66" LONG and you want a warmer too, I would make my firebox and warmer as one. The top of my firebox would be the bottom of my warmer. This being said.... Your firebox could be,36 wide, 26 tall,26 long. This would come out to around 108% I always oversize a little. Your opening from firebox to cook chamber IE (smiley face) could be 9" tall by 31.77" wide. If you stop the baffle plate 9 to 10"s from the end of the cook chamber you will be good. I always try and make the top of the firebox be the continuation of the baffle plate, for a smooth transition of heat and smoke to the cook chamber. If you use a 6" stack go 43" tall if you use 8" go 24" tall. This is just my opinion but I assure you it will work as far as performance and coming up to temp goes. Just trying to help a brother out, aint no secrets here. People helped me and I pass it on. Good luck and pm me anytime and I will help where I CAN!!!!!!!
Your warmer can be as tall as you decide, I recommend drawing the diameter on the floor and decided what suits you it has no impact on the main chamber.... it is a separate deal. I hope I did not make all of this as clear as mud. Pm me if you need to call and I will give you my ######