I have a very early 22" with the square opening that I recently revived to remedy issues I've had from day one. I always fought temps, even with an ATC (old white box stoker). So I just installed a gasket kit, cajun bandit door, and unknownbbq hinge. I did a test cook after everything was installed and the difference was amazing. I set it at 250, then up to 350, then 400 and held it there for over an hour. Then I dropped it back to 250 and held it there for an hour. Finally, I closed off everything and the fire went out completely with left over coals ready for the next cook. Previously, I never once had left over coals; it's a night and day difference from before the gaskets and door. And that hinge is fantastic. All three mods are worth the money, time and effort, in my opinion.
I also replaced the dampers and lid thermometer (filled with water), bought new grates, and drilled a hole for the Weber probe grommet. I know most folks around here cut the rim for their probe wires, but I don't even own an angle grinder, let alone know how to use it, so grommet it is. Next mod is a set of handles. I'm also considering the cajun bandit charcoal basket and some form of wheels wheeled platform (because I would like the extra height).