The 240Z originally came fitted with a 2-row aluminum core which gave up the ghost about 10 years into my ownership of it. Unfortunately, it happened on the highway on the first day of my long-planned vacation one hot summer. Fortunately, I pulled off the highway and coasted to a stop in the parking lot of a radiator repair shop.
The guy installed a 4-core COPPER radiator into the same tank frame my 2-core aluminum unit had fit. He sprayed it black and I was unable to tell the difference even tho I had lived with the car for a decade.
The combination of copper and two additional core rows resulted in a super-cool engine temperature under every condition. Installed about 1980, this same radiator has NEVER allowed my car to overheat since then and when I had it rebuilt as part of my restoration 4 yrs ago, it was reported in grand shape and hardly needed any attention.
I suspect I might have added a few pounds to the car with the weight difference of copper vs aluminum and 4 rows of coolant vs 2 rows, but certainly not as much as the peace of mind weighed.
Frank T