The alternator belt should come off of the water pump at almost a 90. Not enough wrap on the pump and it may slip?
Making the belt to tight to compensate slip may ruin the bearing in the alternator.
The AC alternator pulley would worked perfect. I see your way is easy but I would be concerned about belt slip . V-belts should always have a atleast 1/4 turn of wrap on any pulley.
I guess you'll see how long the belt lasts if it stays on . It may work if you keep the RPM's down. Good luck.
