It's pretty easy to tell from the pictures that Thermalright has made a big improvement on the mounting method with this new heatsink design. The new clip utilizes the OEM AMD retention frame to fasten the Ultra-90 down. The peg in the middle of the clip fits into the hole pitted in the middle of the Ultra-90's base, then you clip on both sides and push the lever down to tighten. It's nearly identical to installing an OEM cooling solution.
It's as simple as that.
Installing a fan.. I was a little confused at first, having only two fan clips and four sets of holes to choose from, but that is what instructions are for.
It seems with the design of these fan clips, that adding a second fan could be a hassle, but we were only given one set of clips regardless.
Installing a fan on the Ultra-90 is as simple as installing a fan on the XP series heatsinks, just at a different angle.