Do you actually need the heat-sinks? I know the 65w and 100w boards they sell just have the driver stuck to the board. If it is just three boards hanging, with the driver outside, woud it work without them?
In one tent I have an HLG260 that is extra wide, and the spacing on them is fine for coverage with a third thrown in. The other is an HLG260 that was bought for a 3x3, and has the boards side by side instead of end to end. At a minimum I would have to cut the heat-sink in two, but if I could just ditch it that would be cool.