Intro and Question (Pulley/Water Pump)

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Good afternoon,

My name is Brad and bought a 1969 C-10 a couple months ago for my son's first car. He has named it Caroline and it has a the CST package, heavy duty tow option and factory roof marker lights. It's a 350, but not numbers matching. We looked for a long time and finally found one in our price range and good condition.

As I own a 68 Camaro, we wanted a truck that shared engines. That was the argument I used to convince my wife we needed another old car. The engine is out and it appears I am at a crossroads regarding pulley and water pump. The current water pump is short, and the pulleys fit. What are the chances a short WP was installed from the factory on a 1969?? I have already reinstalled a slightly used (stolen from the Camaro, so that I can upgrade it) short water pump and now I have a different mounting pattern for the WP pulley and the WP.

So . . . if you are still with me, here's my problem. I would like to keep the short water pump but what pulley can I use that is the smaller pattern? The water pump pulley has three grooves and the crank pulley has a gap between the pulley closest to the engine and the other two. It has power steering, as well, and keeps me from just buying pulleys without first checking out what guys have to say.

Thanks,

Brad