Wait, wait, WHAT?! You're going to get me in trouble here.
Well all I did was open up your mind to the possibilities. You were going to hit a wall with the Haf-X with anything else you'd want to add to it. Say another GPU for the loop which would than need more heat surface etc. Plus you made it clear you hate anything outside the case. I did also bring up the Primo at a more affodable option but you insisted the 900D got you all fuzzy and warm inside. I said hey its your money, do as you may.
Phew.......got that out of the way.
Is that the biggest 80mm rad you have? (I forgot the biggest size of the monsta and too lazy to tab out and search for 30 secs) You better be careful fitting such thick rads in any case. The 900D has lots of room down there but once you go push n pull on thick rads they either won't fit or almost touching. Measurements and plan ahead my son.
Key thing here, look at other watercooled 900D build logs and those with monstas in them. A lot of people don't do that. I sure did on every build log and grabbed a bunch of ideas and made it my own.