Fan shroud question!

[Harpie]

Ok I think I got this figured out but I know you guys can help me out. I swapped in a vortec 5.7 in my 71 and am getting everything ready to fire it for the first time in the truck. Dropped my radiator in (4row) and my small block factory fan shroud is not going to work. The fan is just a little big and I think if it had of fit will be past the fan. So if I'm reading everything correctly is the big block shroud thinner and possibly have a bigger opening for the fan? Hope that makes sense lol thanks for any advice in advance.