I just went through this. I had an original 3 core radiator. I had temps of 220 after getting the car idle for 15 - 20 minutes. After I shut the car off I it went to temps as high as 230- 250. I changed to an aluminum 1 inch 2 core radiator using 20% coolant, a bottle and a half of Water Wetter and distilled water. I'm getting idle and running temps of 155-160 now. So just because HPP says aluminum is not better than brass doesn’t mean you should not consider an aluminum rad.

Consider price. Times have changed. I bought an aluminum direct fit radiator with 1 inch core from Summit for 160.00. Jegs has them too. It has better flow than a 4 core brass rad and costs less. The brass replacement rad would have cost 300.00 plus over size shipping.

Fit:
Obviously Aluminums are not original, so if that's an issue, then start saving your money. Also, I had to make some changes to the fan shroud to get it to fit the rad.

There are many other things you can do as mentioned by the others, but I would look at your radiator then go to things like the divider plate distance.

BTW, you probably already know this but, you should test your fluid's boiling point and your thermostat operation before you check your radiator.

Check out my recent thread "250 degrees in 15 minutes". There were a lot of suggestions and articles offered to assit with this kind of issue.