i thought of that, too... I had just removed my HSF because it was way too loud. .. i could hear the PC from 1.5 rooms away while the TV was on!
i replaced with Zalman AlCu and that works great. Now, i'm hesitant to put it in the xbox.
my 80mm almost fits. i've dremeled the edges and the bottom fits perfectly, but it's still a little thick on top.. maybe i'll dremel some of that too.