The pusher fans on Mercedes cars pull around 21 amps (about .4 HP) and move 2500-3000 cfm, which is considerable. They are adequate to cool a 603 or 602 under most circumstances, but lack the control system for that job. Diesels need more airflow under load than gassers. A gas car at speed can usually get what it needs from natural airflow, not so a diesel. The opposite is true at low RPM.

The problem with a hard mounted fan is that it's horsepower consumption increases with the cube of RPM, although the CFM output only increases linearly. By the time the engine is at 4000 RPM, you're just wasting power. A viscous clutch can save a bit of that, because it's RPM limited to about 3500 RPM. An electric fan requires constant power (and supplies constant airflow) regardless of engine RPM, but may require a bigger alternator. Permacool 19126 is an especially thin and powerful electric fan, there's no reason rescue a fan out of the junkyard.

All that taken into account, I doubt the improvement in power consumption or noise would be worth the effort.