No tension on pully for AC compressor?

I've attached a picture (Series II with Factory AC) of the pully in question which turns the belt that runs the AC compressor.
There is no spring device on the mount and it seems like there should be. You can loosen the mount & pull so the belt is tight and then tighten the mount again and the belt will be fine for a bit, but then it loosens up again and squeals. Anyone know what the right part/part number should be? I've tried one of the suppliers who is having a little trouble and of course I can search XKE engine pictures online until I'm blue in the face, but I'll never get an angle that shows me what I want ;) Any help is appreciated or even a picture of your mounting.

Thanks!