Good move by Freo IMHO if they can offload Dunn and 2nd rounder for Hay. They don't need Dunn, he is another clone of Carr, Bell, Haselby et al.
Acquiring Hay gives them a rock solid defence of Haddrill at FB and Hay at CHB, with Parker or Johnson taking the third tall.
This then frees up Polak to go to CHF, with Pavlich standing closer to goal, say a mid HF / FF, and having McPharlin leading out of the goalsquare.
If they get those three firing up front it will be almost on par with the St Kilda forward line of Gehrig, Riewoldt and Kosi.
Now are they need are some tall and quick midfielders with big motors, an Embley type of player.