That's going to be tough. I think keeping that 180mm PSU is really going to limit you if not make it almost impossible on an mitx build. If you're not constrained by budget I would say ditch the 180mm PSU and pick up something in the 140mm area.
I've been contemplating a Node 304 build just because i've got an extra 140mm 850w PSU sitting around. That's the case I would go with.
From what you wrote I'd suggest to take a look at the Bitfenix Prodigy or Coolermaster Elite 120 / 130 and consider some modding for getting the PSU in.
You might take a look at "Small form factor" subforums for further threads and inspiration.
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