There is a major issue to consider...and as a whole, I agree with the other guys that it'd be easier and more economical to just run both smokers separately.
That issue is a big one: pit builders use strict formulas regarding the ratios of dimensions in a smoker. Specifically, the volumes of cooking chambers, fire boxes, and smoke stacks...as well as the total areas of the air intakes and the throat opening (the opening between the CC and the FB) must all be within a calculated range.
If you're serious of trying this, I'd strongly suggest finding one of the readily available online pit calculators, plug in your numbers for the volume of your extra-long cooking chamber, then see how much the volume of the firebox and smoke smoke stack would need to increase, and how much bigger the air intakes and throat opening would need to be, in order to get this pit to draw air properly and burn wood cleanly and efficiently.
My suspicion is you'll find that the numbers don't add up without doing a major fire box and smoke stack rebuild. At that point, you might realize you could probably build a new, bigger pit from scratch for less work and at a comparable cost.
I don't mean to sound like this is a bad idea. If you're handy enough, and have the metal working tools to do it, it can be done...but it
is more complicated than simply welding 2 cook chambers together.
If you're interested, here's a link to the pit calculator I've been using...pretty simple and straightforward.
The SmokerBuilder® Official BBQ Pit Calculator will help you design and build your smoker according SmokerBuilder's proven design calculations. Ensure that your smoker is sized appropriately and save time and money on your build.
bbqpitcalculator.com
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