The 22RE is a tough engine, but one weakness is the headgasket. Both my Toyota 22RE had head gasket leak at about 100k-130k. Overheating is probably the prime reason for short life of headgasket. The 22RE also does not like to run with a leak in the cooling system even if you keep the water level topped off. Fix the leak. While you are changing the headgasket, it is good idea to change the timing chain. The chain stretch over time, and the tensioner cannot take up the slack anymore. Next is the chain will slap, and break the plastic guide. Use metal backed guides like the ones sold by engbldr.com. If I have to do things over again, I would get all the parts from engbldr. He has good quality parts at good price.
Also, while you are at it, take off the exhaust manifold and bring it to a machine shop to check for flatness, and machine if necessary. Sometimes the nuts holding the exhaust stretch or loosen, which cause the exhaust to warp. If there is a leak at the manifold, air will get into the exhaust, and O2 sensor will not measure fuel mixture right. Use Stage-8 permanent locking fastener to make sure there are no more issue with the exhaust system.
One more thing while you are at it. Replace the rubber "O-Rings" that hold the fuel injector to the manifold. There is an o-ring at the fuel distribution manifold on top of the injector, and another rubber seal at the injector. The rubber seal at the injector for some reason like to crack and leak. Even a new one made by Fel-Pro cracked after about a year and a half. Most likely if engine is ever overheated, the rubber will crack. Replace them first, and ask questions latter.
Last hint, do not use long life coolant on old cars. They attack the solder joint on the radiator and heater core. Use the traditional green coolant, and change it once a year.