FWIW, I posted a couple of threads over the past few years, documenting the problems I had with my car and its overheating problem. See the thread:
To steam or not to steam, that is the question...
I had a stroked 427/484 with aluminum heads and dual Holleys. Driving around in Arizona in the summer was more than the stock brass radiator and anti-freeze could handle. Reader's Digest version is I changed the radiator to a custom-built Griffin aluminum double-row unit, and replaced all of the anti-freeze with distilled water and two bottles of Water Wetter. Water is a better heat-transfer medium than ethylene glycol, and is only necessary if you operate in temps below freezing. I could get away with that because it seldom (?) freezes in Phoenix. Anyway, that resolved my problem; the engine would go up to about 205 deg F in slow traffic and stabilize there, and with the 180 deg thermostat would run about 185 in the clear. You might try to reduce your anti-freeze level and add some Water Wetter before attempting any expensive repairs (a custom radiator will run roughly $800). If you decide to try straight water with Water Wetter, be sure to also add a can of radiator additive to provide the anti-corrosives and lubricants which are usually included in the anti-freeze. The Water Wetter helps because it is a surficant; that is, it reduces surface tension of the water at the interface between the fluid and the water passage, and therefore reduces the formation of steam bubbles in the cooling system, principally in the cylinder heads. This keeps more fluid in contact with the metal and transfers more heat to the fluid, which can then transfer it to the radiator and air flow.