Martin, I've seen the Merc 4-blade with that cast hub. It didn't occur to me that the fan blade would be separate on those, but it must be if the hub is cast. Can't you just use any aftermarket fan with that?
Yes, F-1's came with shrouds, but they got thrown away many times. They make things very tight up front.
So did you have to press the narrow sheaves onto truck type WP's? Isn't that a treat?! I think if my WP's ever fail, I will convert to truck belts rather than deal with that again.