Walter, the early 1275 cars used the down flow radiator, and I never had any cooling problems with them. The crossflow requires a different shroud, and you will have to run the crossover tube that bolts to the steering rack, as well as the separate expansion tank. The 1275 had two different water outlets, depending on which radiator was used. The crossflow setup is also marginally lighter.
If you do go with a downflow type, living in Santa Rosa, you may want to look into having a thicker core installed.
Do you have the '62 radiator to work with?
Jeff