I think you are making the radiator test way too hard by making it a fan test also. You just need a box you hook to the radiator with enough of a blower that can be create a pressure drop from .01" to maybe .5" across the radiator. I don't know what we have in practice now, however based on the fans I imagine it is in the .05-.1" range.

That would be quick, and neat. Then you can just select the fan with a shroud in pull that will duplicate the pressure drop you want.

BTW, what was your room ambient? Did it differ from air in?