Your making this harder than it needs to be. My outlaw has even temps all across the cook surface and it eats 1 split every 45 min.
The biggest problems with this pit are
1.) the top closes in a different spot every time and doesn't seal
2.) the fire box is barely big enough to allow the pit to breath
3.) big hot spot on the fire box side and 100 deg colder on the stack end
4.) POS thermo located in the wrong place
Let me preface this by saying I'm a big believer in using what I can see not seeing what I can use.
1.) place washers on the hinge pins to tighten the hinge
install an Angle iron frame across the sides and back of the top to seal and stiffen 1" A/I was used here
2.) the fire sits to low in the fire box to breath( Fire is a Bottom feeder drawing air from its base up through the solid fuel to give good combustion) cut 6 pieces of Steel A/I 12.5 " long and place them in the fire box top this with a piece of 12 X 24 expanded metal the expanded needs two 90deg bends the first 4" on one end the second 2" on the opposite end. the base of the fire is now in the center of the intake where it need to be build your small hot fire on this.
3.) the Firebox opening is to large and allows the heat to exit go to the top and exit out the stack
remove the two Ci grates that came in the fire box and put them in the oven side 1 in the one at each end.
take the charcoal pan and flip it over on top of the grates. slide it up to the fire box opening. now the heat will stay low in the pit and exit along the entire legnth. this will get you temps with in 25 deg end to end.
to equalize the heat we borrow a little from Horrizion Smokers this will bring the temps to with in 3 deg all across the surface. drill a series of holes in the plate. from 1/4 up to 1/2 " spacing is 6" between holes and 4" between the rows.
4.) install a new thermo that is reliable and located properly ( Stem visible in thesecond pic) mine is centered and slightly above the handle what I call the middle of the Brisket high.