It would be super easy to fix the horseshoe thing yourself if you want to. It goes together in a pretty obvious way, as you can see in the pics you've posted. If I were you I'd do that yourself ASAP and see if it fixes the idling issues you're experiencing.
Did you order the replacement Gates belt that goes with the UD pulley? It's shorter than the stock belt, you might want to double-check it. If they re-used the stock belt it would slip, which might cause some of your idle issue as well.
As far as voltages go with the UD pulley: With the engine warmed up and idling in neutral, it should be at least on the 14 mark, if not higher. Mine will dip pretty low (not quite to 12) under certain conditions briefly, but it never stays low. "Certain conditions" being things that suck more amperage, like the end of the power window auto-up and auto-down movements.
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