It's not really impossible like everyone else is saying, but it will require alot of work as well as some serious soldering skills. You'd have to use a slim as the innards for the fat are too tall for the 360 Chassis.
-Use USB extension cables and a HUB to setup the connections where they actually belong.
-I said HUB because you're going to need to run the HDD as an external USB, but removing it's original enclosure and putting it in the 360s HDD enclosure.
-Need some plastic molding skills to close up the excess holes (the original AC port will need closed off to keep dust out.
-You'll also need a dremmel for the disk drive so you don't have a hole where the drive would be. If you want to play hard copies of games, you'll need it to also make a flip top mod for the hard plastic casing.
-You'll need to make jumpers on the ps2 AC circuit board to bypass the power button, ground, and of course it's draw and move it to the respective places on the RF modulator from the 360 (which you'll need to remove the plug prongs from the back of it)
So before you actually go to do this, make sure you're capable otherwise you'll be wasting a fairly large lump of cash.
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