Fan Clutch Replacement Process

As always, I come up with what is probably a dumb question...67 Camaro SS350, except not the original motor (it's a '72 vintage I think). Anyway, the fan clutch obviously isn't working, and the one I bought to replace it, which is about 7-1/4" O.D., isn't compatible with the fan (the mounting suface diameter in the new clutch is too large for the fan). The clutch that was in it is about 6" O.D. The new one has mounting slots, where as the old one has holes....the slots on the new one do align with the old one if you hold them up against one another. Also, the pattern of the fins is alot tighter on the old one than the new one.

So, I would be forever grateful if anyone could identify exactly what was in there, as the overall swap would be easier if I could find the right clutch!

Could the old one be the Short pump version?

Thanks in advance!