Which Fan Shroud do I need?

[Eotku]

I have a 1970 4x4 blazer that is pretty much stock. When I got it there was no fan shroud. The heater core started leaking so I am going through the whole cooling system. When I took out the radiator I can see at some point someone replaced the original 3 row (my blazer is a 350, Auto, NO air conditioning) with a 4 row radiator. I am having the original 4 row tested and repaired and now want to buy a fan shroud and wanted to know which shroud I need to get. Are all 4x4 shrouds the same?