I recently spoke with a local shop about doing this. I've had them do work before and been happy. He explained how they would do the four row by splitting the corners of the tanks to widen it. When I told him I had a spare radiator that had pin holes all over the tanks he said, "No problem, I can get new tanks made." I didn't inquire as to cost and haven't been back with my other radiator yet to ask any more questions but I would assume this opens the possibility for a completely new radiator with tanks designed to accommodate a four row core. When I take my radiator in I'll ask more questions and post the answers.