I got the 6.0 fan installed. It was pretty easy. The hardest part was to get the fan shroud out of the way enough to get the 7.3 fan out and the 6.0 fan back in without removing the radiator.
I can tell a difference in the amount of air moving when the engine is below temp and idling.
The 7.3 fan blade setup weighs in right at 10 pounds where the 6.0 fan blade setup weighs in at 6 pounds. That is quite a bit of weight reduction on the front of the engine.
The research I've done says the 6.0 fan blades flow 10,000 CFM (can't confirm) while the 7.3 fan blades flow 5,000 CFM (can't confirm).
Here is the 7.3 fan laying out with the fan clutch still attached.
Here is the 2 blades side by side. Notice not only that the 6.0 fan is plastic (except for the center hub) and the the 7.3 fan is all steel. Also notice that the 6.0 fan has blades evenly spaced 360* around the hub while the 7.3 fan doesn't.
Here is the 7.3 fan clutch bolted up to the 6.0 fan blades. There is no modification needed to bolt the 6.0 fan blades to the 7.3 fan clutch. The 6.0 fan blades have the same clutch bolt pattern that the 7.3 fan blades do.
Here is the 6.0 fan installed.