Are we sure it's overheating? You could possibly have a bad temperature sending unit. use an ohm meter, the sending unit should read from 0-5 volts, 0 at cold, 5v is overheat. so if that motor is barely warm but it's showing 5 volts the sensors bad. If it's actually running like it's overheating, and your sure it is, try retarding the timing if it seems like it's worse, then advance the timing. Easy to do, losen the holddown clamp on the distributor, enough so you can turn the distributor counter clockwise and clockwise while it's running. if the timing is too advanced it causes a lean condition, which will overheat it. as you turn the distributor back and forth, one way will cause engine speed to increase, the other will slow it down. Find a spot where the idle is reasonable around 5-700rpm tight the distributor and try it. I would say use a timing light, but since I also experienced this problem on mine, when it was timed according to spec it would run hardly, probably because the distributor was a tooth off, the points were bad, or the timing belt jumped a notch. hope this helps