some radiator questions

Hi there,
I am needing a new radiator and both fans, but dont feel like paying 190 bucks for both of them. I found some other "High Performance" radiator fans but hey come in a few different sizes.

Mine being destroyed and all i cant measure the diamete of the blades. Does anyone know what size will work in the size to replace the stock ones? also is the shroud thing necessary or not? Anything i should know before i go off and do this?

Thanks,
Nick