Pontiac Firebird Serpentine Belt Pulley

I Had My Idler Pully Come Apart On Me. When It Flew Off, It Hit Something Directly Over The Oil Filter And Broke It In Half. It Looks Like...

I Put On An Idler Pulley, The One Above The A/c Pulley Not The One On The Belt Tensioner, And When Removing The Old One The Threaded Metal...

I Was Told There Is A Problem With The Idle Arm Pulley And The Original(metal) Ones Are Not "grooved" To Hold The Belt On. I Can Not Find...