[grumpyunk]

Working:I run mine with one radiator blocked off with a piece of inner tube rubber that I cut to fit and wedged in between the radiator and the plastic rock deflector that snaps in front of it.

Have you considered running with smaller pieces of inner tube on both radiators. You would get more uniform coolant temperature between the two, and less temperature drop in both that you get blocking one. The coolant on both sides would loose heat rather than circulating hot coolant on one side and cooler on the other. I have no idea of where/how the coolant returns from the radiators and whether it merges the two flows before entering the water jacket. If the coolant goes to two different places, one may assume the bits inside are not getting equal cooling. More or less.
tom