If you want a stock style set up then use the Extreme but if you dont mind not having an oil cooler or plan on using an external oil cooler then go with the fbody.
you will be fine with the fbody just add an external oil cooler later if you feel you need one. you also need to check the air boxing around the grill to radiator it may be gone this will make the car run a little hot as well with out it the air can go any ware it wants in stead of forced threw the radiator. check it out here. GNS
Right now I'm with the stock radiator and if I stand still for like 5 mins or even less it goes up to like 200+ and if I'm driving at around 50 mph it stays around 175-180