I hate to be critical, but there should be some fore-warning on this guide. It voids your warranty, and any chance of Sony servicing the console. In my opinion, this is a repair that only a company with BGA rework equipment should do. Any DIY fix will last a very short amount of time. (I've experienced it myself - trust me, I've tried on many xbox 360's)
Never seen the V-Ram on the substrate before - won't that make GPU replacement pretty expensive?