My fins were not the issue. I was talking about the tubes themselves. When pressure testing the radiator to much pressure expanded the tubes, So much that it restricted air flow. It could not be seen by looking at the radiator. But light would not pass through it or air.
The only other thing that could cause overheating that you have not talked about would be severe lean condition caused by to much air and not enough fuel at RPM's. . Or timing retarding to far at RPM's. Or Cam timing?