I'm admittedly not familiar with Powerdyne's bracketry, but it does appear to be slotted just for that reason. Do the Powerdynes not come with their own tensioner?
Yes, you loosen the bolts and slide it down. It is a pretty crappy setup and you can push the downward belt into the upward moving portion if you adjust it too much.
Tighten the bolts snug (not super tight), take a small wrench, put lip of bracket in open end of wrench, bang on wrench with rubber hammer, tighten down bolts. Had to do this with our Vortech on Saturday, took about a minute to complete.