1987 Honda Civic Cooling system problems

This 1987 honda civic has been sitting for the last 9 years, and we just recently fixed it to run. In that process we replaced starter, clutch, water pump, timing belt, and others. It ran fine for a couple months. Then it started overheating and noticed that there was a big hole rusted out of the radiator. We proceded to replace the radiator, and flushed the cooling sytem. Then it worked fine for about a year after that. Then it started heating up again. We tryed everything. We checked the thermal switch(b/c) the fan never kicked on. It was fine. Then we replaced the thermostat because it seems like it was getting stuck. We also replaced the upper and lower hoses. We ended up removing, putting in new antifreeze, and flushing it like 6 or 7 times through the whole process. We tried bleeding it as well, but no luck. After we bled it the first time, the heater work for a little bit right away, but then started spitting out cold air again. We have tried everything we think. Any suggestions of what we can do? I am desperate. It is really making me mad, and I cant figure it out. Thanks a lot guys!