You might also try running with less anti-freeze in your coolant mixture.Water actually transfers heat better than anti-freeze.The more water you have in your mixture,the better it will cool,but this also lowers it's boiling point,so it's kind of a "catch 22".I myself run strait water,with a rust inhibitor added,this has worked good so far for me.
Also do you run a shroud?This can also make it run hot if not set up right.
One question,you say the radiator "overflows",do you mean BOILS over,or overflows out the overflow tube.A coolant recovery can can be used if you are worried about the overflowing out the tube.If you mean boiling over this should not be happening at that low an engine temp.
67 RS RAGTOP # matching
4X4 Chevy truck