This has probably been covered here before but here goes anyway.
I replaced my '70 Nova 2-row radiator with a 3-row, and then found out it left no room for the fan blade. So I needed a shorter water pump. This is how you can do it: Press the pulley flange down further on the shaft and use a small block pulley 69-85 for LONG water pump. I used a single groove pulley.
Do not press against the impeller, use a small socket to put the load against the shaft instead. And a deep well socket to slip over the pulley end of the shaft, 15mm seemed to work well. The shaft will slide into the socket while the socket pushes the flange down.
Once done, cut the shaft down if the tip is in the way. Leave some exposed for centering the pulley.
