Alluminum dissipates heat quicker than brass or copper. I'm not a big fan of plastic tanks but they've come a long way with these tanks. I've got a 350 in my '63 with a brass core radiator. I haven't had any problems with the truck overheating here. As soon as it warms up and the thermostat opens, I'm running at 180 deg constantly. A couple things may affect your situation differently though. You're running an automatic without overdrive. You're not towing much weight. You could try it as is and risk frying your tranny or motor. I only tow a couple quads occasionally. If I were towing with a TH350, I'd spend the extra bucks for an alluminum radiator. They're easier and less costly to repair. Just like everything else though...it's only my opinion.