Tried the idler pulley for a short time on my '85 after the pump fell apart and it cratered (real P.O.S., I won't even mention the Texas based company's name...). Belt I use now is a Cadillac application, but I forget which one off the top of my head. I'll try and check the numbers this evening. Have had no problems, but I rerouted it based on the underhood diagram, and drew up a new one that kept the accessories all running the same way. I redraw it each time before I change it now to be on the safe side.