Cody many people use a 302 style radiator because cross flow is supposed to cool better and such, rumor has it that Ford went that route for a reason. so you should be able to go that route with the conversion pump, but dont forget to double check your pulley alignment and clearances.
Do you need a new radiator? If not look at your costs involved before you commit down a path, it gets expensive fast, even if you get that radiator and keep your timing cover you will need to deal with the dipstick to go in the timing cover because you cant use the pan that the 5.0 uses, so that means drilling into that cover. You will also need to use an electric fuel pump, no biggie if you are going EFI, but for a carb its overkill.
If you can find a 289 timing cover with a pointer on the drivers side you can use a 289 water pump and keep your current radiator, look period correct and save money.