Completed install over the weekend, added the sensor ground to the radiator and got it reliably switching. Today I took it out, its only 70F outside so not a brutal climate.
I started easy and made sure the fan would go in and out at temperature and then ran the car hard through several acceleration runs and pulled to the side and let the car idle, worst case scenario for the cooling system.
It performed really nice, fan came on immediately as the temp spiked from the hard runs. Watching the gauge, the fan stopped temp rise in its tracks and then took about 90sec or so to pull it back low enough to kill the fan.
I went with the 4239063M (Combo/Black) 1963-1972 Aluminum Radiator, the engine is an L76, but has been rebuilt with hydraulic cam and lower compression for crappy CA gas.
Tom Dewitt had explained that it has a slightly lower cooling capacity than the stock unit had (and their resto radiator has), but my car already had an older copper/brass replacement (which was seeping coolant in a number of places) and was probably lower already.
All I can say is that so far this radiator looks like a winner !