With the pulley setup and belt you have, which direction would it turn the pump? That's the deciding factor. If the stuff pictured above is yours then yes, a reverse rotation pump is correct.
A friend once bought a '72 C10 with a Vortec 350 & overheating issues and he eventually cracked a cylinder head. Once we started looking we realized that it had the Vortec pump (CCR) yet the truck had the original serpentine setup. When we removed the pump both passages were completely corroded shut.