Could you take a few pics of the stock heatsink detached and show a pic of all the heatsinks attached(before the main cooler).
I remember issues with 7970(or maybe 6970? it seems ages ago I just can't remember how long ago
) heatsinks, the AC ones IIRC that people were using and didn't realise there was an extra chip that needed cooling and a few cards died. From the pics I saw a while ago of a 290x it looked like there was one extra chip that needed cooling or at least had some frag tape on, but sometimes it's there as an insulator rather than cooling.
AFAIK prolimatech aren't officially stating support for the 290-x on the cooler?
EDIT:- shame, they've done away with the fan bracket and gone with the extra weight all attached to the heatsink/card instead. While it's easier, the fan bracket was a much "safer" way to go about it. For such an expensive cooler it would be nice to have the clips and the bracket so you can choose.