The tensioner and idler pulleys all have normal right hand thread bolts, i.e. no left hand thread. Provided you are able to cut the bolt, just taking the head off should make remainder much easier to get out since the clamping force is now gone. If you haven't destroyed it yet, you could always chance that one part and leave it on if it still turns smoothly. Be a shame to waste a good part though, especially with the attendant damage it might bring on fail.