Duster overheats with 26“ Radiator

Nice car! Does it overheat in traffic or on the open road? That radiator should easily cool your engine. Did you have the original radiator recored? It is possible that the waterflow through the radiator is inadequate. You might want to use an infrared thermometer and check several areas of the radiator to see if there is consistent temperature drop (hotter at the top and cooler as you go toward the bottom).