7 blade fan question

Don't know the PN, but a mechanical fan doesn't fit a thermal clutch. Clutch fans are much different, w/ a big center hole. Someone might have installed a special "clutch eliminator" stand-off.

If the fan was the cause, then vibrations would be noticed just revving the engine in neutral. I once had a bad U-joint in my 69 Dart. I got a slight vibration at 55 mph, then went away. The U-joint was totally rusted and loose, w/ no more needle bearings. I guess that is why I got a clunk when shifting into R, for ~4 years before I found it.