Took it for a test ride and the head gasket seems to be holding up OK. The motor is getting quite hot, but not overheating. It's still got a lot of pressure in the crankcase, and after talking to a couple people, the only think I can think of is that something is up with the timing...Either valve or spark. Apparently the CDI units go bad on these scooters all the time, right?
Also, the fan works if you jump the leads from the switch unit that threads into the radiator body, but it never turns on. If that sensor is dead, can I just install a switch between those leads, and manually turn it on whenever I ride? The system still has a fuse for that circuit, so that should be safe, right?