The planning stages were working out which screws were unique to the GPU block and which were shared with the backplate, and in turn what the screw lengths would be given Watercool and EK do things differently.
So we ended up with 7 M3x8mm dome head screws to fix the block around the GPU, which were shallow enough in head size not to interfere with the spacing on the backplate. We then had 4 M3x12mm countersunk screws to mate the backplate with the remaining 4 holes in the block. Add 2 M3x5mm at the very edge of the PCB to secure the backplate and we're all done.