I used one of those old style DD Geforce 2/3 blocks on my Radeon 9700 Pro; it has standard holes I believe (I previously used it on a Geforce 3) but I did apply a slightly thicker layer of thermal compound to make sure there was contact, due to the shim that comes on these new Radeons. I don't know if there is any such shim on the card you mention.
No idea what the temps of the GPUs were but seemed to be working stable.
As an aside, does anyone know how big a difference there is between the old blocks and the new in terms of performance?