Hard to tell if it will work , but if the side of the smoker is flat and the side fire box is flat . then you will have to cut out the hole on the firebox
(should be able to punch it out. Should be a football shape when done. ) and then on the smoker cut a hole to match the side firebox hole.
then just bolt it together. Just check Home Depot . They have a firebox made by brinkmann. I would think this should bolt right up to it (not sure) but worth checking out. You will have to take the shelf off.
( Use this Brinkmann Off-Set Firebox Smoker with the Brinkmann Dual Function Grill and Smoker units)
http://www.homedepot.com/buy/outdoors/outdoor-living/off-set-fire-box-accessory-88933.html
hope this helps you some.