What car? Is this for a turbo or supercharger application? If not, then it's probably not worth the effort or expense. As an in between option, you could get an electric water pump which eliminates the pulley and belt.
But to answer your question - perhaps the image below would give you an idea? This is a small block engine plate that AR Engineering sells. Far as I know, he does not specifically sell the water pump adapters but maybe you could ask him (AndyF) about them. If you are trying to use the stock timing cover with fittings like shown below, you'll obviously have to get creative.
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