I wanted to upgrade the cooling from the stock Alienware liquid cooling, so I ordered one of the H80i with the knowledge if it doesn't work, I can send it back (Amazon). Many said it wouldn't work or that a fan would need to be pulled, but I made it work! Just note, you have to keep your top piece off of the machine afterwards - you sandwich the top fan on top, and the radiator and bottom fan where the original was. This is not a problem to me, as I keep it stashed and I had the top piece off to begin with -- even with stock cooling, it cools better without it holding in some heat/blocking some airflow.

Here's the end result (I have all panels off at the moment) - https://imgur.com/a/afHb9oU

Hope this helps some of you, and remember - if you're going from air-cooled to liquid-cooled, you NEED to install the heatsink/s on the VRMs (at least the one bank) or you'll be getting a new motherboard in short order. This is not an 'optional' thing, if you use the machine heavily.