Originally Posted by Stretch

I'm trying to understand what the heck is going on too.

It sounds like the new pump bolts up to the engine but the pulley does not fit - and it does not line up with the existing "lines" in which the belts have to run.

First step =>

Compare the "heights" of the water pumps - does the old one stick out further from the block?

There are different pulley options out there - you could be suffering from a bit of a swap around