This is kind of a two-parter.
1) I bought a 68 GM fan clutch a while back and put the aftermarket fan I had on that. The fan was kind of universal, so it fit this clutch. I didn't really pay attention but I found that the fan clutch spacing, on the fan clutch, was only 3". Does someone make a repo or does GM have a 3 1/4" fan clutch?
#2) I finally found a fan that is an 18" 5 blade fan like the original Z28 fan with a 3 1/4" fan clutch spacing. But it has 5 rivets instead of 4. What could this be for?