The water pump pilot is .675 and the fan side is the more standard .625, So it's an oddball. I was trying to mount a newer GM fan clutch when I discovered this.
Here’s Hayden’s catalog as a pdf. They show both the 21045 (SD) and 215046 (HD) for ‘59-69 Buicks. One has a .63” hole, the other is .75” with a bushing that reduces it to .63”. If your water pump is .675” it may be made wrong(?). I guess you could have a bushing made for the larger holed clutch (or turn down the wp shaft?). https://www.haydenauto.com/media/5587/imperial_fan-clutch-pages.pdf Patrick
I have the non clutch setup. Only the AC cars had a clutch in 61. Everything I have is all factory stuff. The AC water pump which is a different part number looks to have a different size per your link. If I decide to run a shroud I will need a short spacer.
