There are shrouds available for the 64 small block radiator because it uses the same radiator as a 66 Fairlane. They are plastic repos and run about $100. The place I saw them was from Mac's although I do not recommend you tell them you are using it on a 64.
I built a T-Bolt replica with a 427 FE and they listed shrouds for 63 and 64 Galaxie with big block (the same radiator the factory used in the T-Bolt) but I made the mistake of asking them what was the difference between the 63 shroud and the 64 shroud. Instead of answering my question they ask what I was going to use it on, when I told them they refused to sell me one because I was not using for the right application.
I think they are a bunch of dumb a-s h-les telling me what I could and could not bolt it onto.
I later found out that the only difference in the two years was the spacing of the mounting holes which would have not effected my use since I built a custom radiator for my car.