isnt 3/4" MDF a tad heavy to just hold a radiator and a pump? Or is that just what you have laying around?
Id go the dual PA160 and dual 1048s route. 2 PA160s would outperform a 120.2
If you dont care about the $$$ difference go with the 160s. As for pumps try silentpcreview forums for threads on which pump is quietest. I think the 1048s are still held to be the best. A D5 would give more pressure though.