So, what started out being a quick removal of the air filter housing / rear fender in order to install a replacement carb -> filter housing air box turned into removing the swing arm and all the ancillary bits, cleaning off 33 years worth of oily mud and muddy oil, and then priming and painting lots of the bike.
Spoilers; eventually I did install the replacement air box.
In this page from the service manual you can see how the air intake system works. My biggest issue was that what is labeled the air cleaner chamber was melted and smashed in where it joins with the air filter housing / rear fender. I was able to find a good replacement on ebay, and it was immediately obvious that the one on the bike was a mess.
However, to do it right, I felt that I needed to remove the air filter housing / rear fender. To do this, I needed to disconnect the shocks and lift the back end of the bike in the air to give myself enough room to remove the housing. Of course, there were about 1,000 other pieces that had to come out first, like the battery and the rear chrome fender.
Once I had the air filter housing out, I discovered that the crankcase ventilation hoses were hooked up to the wrong spots on the air filter housing. Huh, having the valve cover vent going into the wrong spot can't help anything, and no wonder I never got any water out of the condensation trap drain!
At this point, I was feeling saucy, so I decided to partially strip down the bike and get some paint on the frame. It was a beautiful sunny day, not too hot, perfect for painting. I removed the rear wheel and then pulled the swing arm. The next step was cleaning 33 years of grunge off the swing arm and rear wheel, and cleaning 33 years of chain lube out of the drive sprocket housing on the side of the transmission. The chain, a non O-ring unit from DiD, got a dip along with the sprockets in some 87 octane. The swing arm and the sprocket cover ended up in there too, as there was a lot of crud caked onto those parts.
The engine and center stand were cleaned on the bike, and really shined up nicely. I took the wire wheel to the swing arm to get some loose paint and surface rust off of it, and then wiped it down with acetone. I hit it with three coats of self etching primer, and then with two coats of satin black. It ended up looking sharp!
I also cleaned several areas on the bike where there was surface rust, and hit them with the self etching primer and the satin black. There was no bad rust on the bike, only some surface rust from being outside. Someone took care of this bike at one point, but it had become neglected in its later life.
After the paint had dried, everything had to go back together, starting with the swing arm and rear wheel. I lubed the swing arm bushing while it was off the bike, as the zerk fitting is hard to get at on the underside of the swing arm. Everything went back together well, except I discovered that the right hand exhaust mount was bent, causing it to foul the swing arm at full droop. I straightened that out, touched up the paint on the swing arm, and finished that up.
Now I could actually install the new air cleaner chamber, along with the air filter housing / rear fender. Everything went back together nicely, and for the first time since I've had the bike, the carb boots slid right into place. I reinstalled the plastics, seat, and tank, and had a bike again!
After some fiddling, the bike fired right up without the choke. Hmm. It is running pretty rich, which is about right since the 90 main jets have been replaced with 110s, and the air box is now leak free and almost all stock, with the exception of the air filter cover being missing. I think I'll try 95s or 100s and see if the bike stops fogging for mosquitos.