you need to wash the radiator good with dawn soap and water, or simple green and water. then degrease, epoxy, and paint. refer to the tech sheets for propper application...
as for the car body, if it wasn't washed to neutralize the soda, before the epoxy was applied, you need to strip it and start over. doesn't matter how long it has sat with epoxy on it. if not, after paint, once it gets in the sun good tiny bubbles will start to appear in various places over the car. those could lead to bigger bubbles. even just a few hours in the sun can cause it to start bubbling. even worse, you start to lose adhesion of the epoxy to the metal.
something you probably dont want to hear, but its the truth.