1991 Tbird - How to Put Tension Back on Belt After Alternator Replace

[Samsco]

I have a 1991 Tbird V6 that I just had to replace the alternator on. Removing the idler pulley next to the alternator so that I could remove the serpentine belt and remove the alternator was simple enough. I have the new alternator on and the serpentine belt back on.

The problem now is to put the idler pulley back in place. There are two stubs in the housing which have to line up before the housing will seat properly and the only way they will line up is when there is tension on the belt. It seems difficult to keep the tension on the belt while tightening the hex bolt on the tensioner housing.

Can someone give me some tips on how to do this? Thanks.