cast iron water pump vs aluminum pump

got a 340 in a 65 Dart GT ,it was partly assembled so I don't know whats all in the engine. It overheats after about 20 minutes of driving, have tried 160,180,and no thermostate, 3 core 22" aluminum radiator, with flex fan/and shroud,and even a 16" pusher in front. still slowly gets up to 230f. gets there quicker in traffic. It has a 5" crank pulley and about 7" water pump pully. Will a newer style aluminum water pump help my problem?looks like they use bigger dia crank pulleys and will the the 1970 up crank pulley bolt up to my old balancer? I know the inlets will be on opposite ends and timing marks will be blocked by lower hose and I will probably need another radiator but I am getting desperate. All I know about the engine is it has a big flat tappet cam , Venola pistons, eddy dual plane intake and stock cast exhaust manifolds.