There is a difference in the type of clutch only. They will bolt on, as long as the wp shaft size is the same as the clutch. Chances are, you don't have the original water pump on yer car anyway. I would measure the shaft size, and maybe the bolt circle, and see what will fit. Most wp shafts are 5/8" or 3/4" but some are a bit smaller. Maybe they thought you were looking for a "stock/original" fan clutch?
Ron is right, tho. If the pump shaft and the clutch center is the same size, the slotted bolt-hole type will work fine. It's the shaft it centers on anyway, not the bolts.
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