Water Pump Info
There are two distinct water pumps. We will call them the early and the late. The early pump has a short stub end and no left-handed screw at the end. The later pump has a flange with two machined steps on the front and a recess on the back. There is also a left-handed Allen screw on the end of the shaft. The later flange has a smaller diameter hole and the shaft has been turned down. The early pump has a thicker much stronger flange.
The pumps cannot be easily interchanged without replacing the water pump pulley and crank shaft pulleys. The later pumps have the spacer block that fit between the pump and the block lining up the water pump pulley and crankshaft pulley on the later cars.
Water pumps have become very pricey from the normal sources. My local parts place got me a Cardone part #99-5710 for an early style pump and it fits perfectly. I do not have a part number for the later style pumps as all of my cars are early. Another option you have is to find a water pump rebuilder and just have your old cores rebuilt. I have had several rebuilt from a local auto parts store and had no problems what so ever. Keep your old cores even if they appear unrepairable to you. A good rebuilder can repair just about anything.