"Alloy rad" would mean aluminum. So long as the engine will stay cool with an aluminum radiator, there's nothing wrong with it. Copper radiators are popular for racing applications because the engines are tuned way beyond what the power range a street car will have, often times with high levels of boost if it's a turbo motor. More power = more heat. Also sometimes the grill/louvers/duct size will be traded for aerodynamics and a copper rad can come in handy there. On stock cars they may only run a small slit (the rest of the grill being covered with tape) on a speedway or super speedway so a copper radiator can come in handy there (though most of the time they still use aluminum).