I agree with E Paul. If you can get an aluminum radiator, that would be the best way, but failing that, you might want to consider having a new one made from scratch rather than recore the radiator you have. I went that route when I was first building my car. I wanted to make sure my radiator was in good shape and the guy was appalled at how inefficient he said it was. He had built some radiators for some race cars so I had him build a new one for me. I replaced it with an aluminum one because I thought it might be even better (I also didn't appreciate how the temp gauge is graduated so it wasn't getting as hot as I thought), but I'm not sure I can tell that much difference - other than it looks REALLY good! It was over fifteen years ago and I have no memory of how much it cost, but it's something to investigate.