This fan shroud kit from Northern is for use with engine driven fans on Northern "Race-Pro" and "All-Pro" radiators, although it can be made to fit other brands as well.
It's made from lightweight .063" aircraft grade aluminum and has an adjustable collar that can accommodate fans from 15" to 20" in diameter.
The Z40023 will work equally well on both cross flow or down flow style radiators and the shroud comes with all necessary hardware and complete instructions.