'64 A-bodies all came with 19" wide radiators from the factory. The factory A/C car got a 3 row cored radiator, but, I don't believe they had a shroud that year on the V8. If they did, I've never seen one. I would use a rigid 6 or 7 blade fan blade....no flex fan. If your engine runs cool enough at speed, the flow is probably ok, and it's mostly an air flow issue at idle/stop. A mismatch on pump/pulley combo can have an effect too that can be masked at higher than idle RPM. As a rule, the non-A/C cars used an 8 impeller pump and a larger diameter water pump pulley. The A/C cars used a 6 impeller pump with a smaller diameter pulley. Seems backwards eh? It has to do with water flow. The non-A/C pump has more impellers, but, spins slower than it's A/C sister, which spins faster at a given RPM. A mismatch can have strange results sometimes....but not always. I've seen 8 impeller pumps have no problem on A/C cars, and others that had cavitation issues with the coolant foaming up to the point where it wouldn't cool properly. The opposite can be true using a 6 impeller pump on a non-A/C car where the flow is inadequate. It also has an effect on the fan speed if you have the wrong pulley combination. The '64 A-bodies with a V8 had one strike against them with that small radiator, which was improved to the 22" radiator the next year. Converting isn't all that easy, but, I've seen it done. If I were you, I'd probably go with a heavier duty radiator, 7 blade rigid fan, and fabricate a fan shroud for better air flow at low RPM. This is all assuming that the engine cylinders weren't bored too thin and is running with the proper air/fuel ratio.