So you could essentially:
a) use the existing smokebox charcoal pan, flipped, as the reversing plate, butted up against the firebox side, with an adjustable bracket to bolt it tight against the opening
b) move the stack to the other side, next to the firebox
That would accomplish roughly the same thing you see in the CharBroil mod link. You could further:
c) build a flat-top rack of steel strips, it would be supported by the charcoal pan
d) rest water/drip pans atop that rack
That would stabilize temps and provide moisture. If you clean the inside of the top frequently and put in clean drip pans for each session, you could even use the drip as your mop liquid! Use only 3 of the 4 cast-iron grates, leaving a small gap between each. Dip your mop down between the grates into the drip pan, and then use it to mop the top of the meat.
The material purchases required are small. A 4x4" plate of sheet steel to cover the old stack hole, the steel strips for the rack, the 3" flex hose to bring the stack down to the grate, a pair of good thermometers, and of course the requisite pig to cover the old temp gauge hole. Aside from cutting the new stack hole, the work involved is minimal and easy.
Yeah, the plan's coming together. :D