Belt guidance

Just to be sure that you know - using that factory non-AC water pump pulley will realign your belt grooves for the system that is shown in post #18 - the water pump and alternator on the crank groove toward the engine and the Power steering on a belt of its own in the crank groove toward the radiator. You can then use 1970 stock belts. No the system does not have to be stock. The belts on one of my 1970 Darts with a 318 are designed to work with a retro fit Classic Auto Air AC set up which didn't fit as delivered so everything is moved around on the front of that motor! What was important was that the pulley diameters were the same as the original AC system and each belt ran the same things as the factory system. None of the pulleys used were "correct" for that motor. The end system does have to spin various things at the right speed. AC water pump pulley is smaller and therefore spins the water pump faster that the bigger non-AC pulley.

If the altered alternator pulley currently lines up with the crank groove toward the engine, changing the water pump pulley will mean that all is in the configuration as the factory had it in 1970 but then the belts are really different from the custom measurements that you found. Are you using a long straight edge to make sure the pulleys align rather than your eye?? If things are off a little bit some washers should allow you to get it perfect.