i have a 947U on my NF7 S rev 2 right now. it fits snug against the compacitors on the left side of the socket but it doesnt interfear or damage them at all. 100% compatable.
the 900 is wider than the 947, and the 900 still fits. thats a guarentee that it will fit, and also, thermalright has a list of compatable boards for their heatsinks. 947u is listed as COMPATABLE