It will fit fine, however, you will want some kind of support for the heatsink, because the thing weighs a tonne as it is made out of 100% copper. Doesn't have to be anything fancy, some sort of strong string holding it up would do, anything to take some of the weight of the motherboard, otherwise chances are, the board will get warped or worse yet, cracked/severly damaged. a ~2kg block of metal is a hell of a strain, even with a backplate on