I'm almost positive that the EK Asus1 Mosfet blocks don't fit the Maximus series of boards, and that you need the 3a series because the regular 3's have clearance issues around some of the caps. I can, however, verify that the 3a's fit the motherboard with no trouble at all. You will definitely want to get the backplates though, because the board will try to bow without them. If you check out
this thread, you'll see a whole bunch of people who have trial and error-ed their way through this exact same issues.
For the Northbridge, you may as well just grab the matching EK block (EK-NB S-Max), although there are a couple other options as well. The DD Maze 4 also works, IIRC. There's a MIPS block that will work, although availability is lousy, I hear. Regardless, if you drill out the holes a little wider and stick a piece of foam on it, the backplate on the stock cooling system can be used for aftermarket blocks without any trouble.
The PA120.3 will probably laugh at that heatload. My own chipset is cooled by a single Swiftech rad and a single 800rpm fan, and the exhaust air is barely warm. Which leaves most of the rad for the CPU.