To get this block to fit, all I had to do was move the mount posts very slightly, the 4 (actually 5) around the die match up perfectly. I added the 6th, and the one closest to the water IO ports.
I DO NOT recommend drilling to add that mount closest to the water IO port, directly underneath that is a screw that holds the front of the block on (the acrylic). I drilled a hole, added epoxy and then screwed in the threaded insert, and I never saw the screw from the other side, I thought I was just beside it, I was sure if it, but now I can't undo that screw, it feels tight and scary. I probably can't take the block apart to clean it out now, not without looking at it all very closely and carefully. It wasn't even necessary that I add that thread, even if you do want it, you could just glue down a nut, you dont actually NEED to drill down there.
You may notice the copper colour, and "damage" to the block. This is where I was having trouble with fitting the inductors in, but it turned out to be something else, the inductors actually fit perfectly and don't require and additional butchering to fit.
The waterblock is Bykski A-XF6900XT-X for XFX Merc 319 6800XT and 6900XT (but also fits their 6950XT).
There is actually a Bykski water block for the PowerColor Red Devil 6950XT, it is model A-PC6900XT-X.
I bought this model because it was so cheap.
When I bought the GPU, I had a choice of this or the XFX 6950XT, and I REALLY regret buying the Red Devil, it's terrible, the coil whine is like nothing I have ever heard before, from any product, ever! The XFX actually has a better PCB too.