lot of over heat problems can be attributed to timing - or lack there of. If the motor is pretty stock, you should be running around 12 degrees initial timing ( checked with vacuum plugged ). Put a 180 stat in it. Assume you checked things like fan to rad clearance, fan clutch operation, Belt tightness, you are running a shroud, etc. You didn't say if the overheat takes place mostly at idle or at speed. If it's at idle, you are probably not pulling enough air through the rad. You can also try switching your vacuum advance from ported to manifold vacuum. This often helps idle overheat problems.