The fan & clutch mating could be a matter of the clutch's ability to engage the different mass of the metal vs the plastic fan.

It could also be the RPM limit of the plastic vs metal fan as the clutch has an RPM limiting feature (does not run the full/max. RPM of the engine).

Personally, without knowing the specifics on each fan and clutch, I'd lean toward keeping the plastic fan with the matching clutch and metal fan with its matching clutch.

BTW, the 350SDL also had a plastic fan, is the clutch the same as the 606 or the 603.96x? I believe that the 602 metal fan is different as the 602 metal fan has even spacing between the blades and the 602 blades are spaced irregularly. I bought a new OEM clutch for my 602 turbo for $180 about a year ago.

__________________

Gone to the dark side

- Jeff