I just picked up a mint 65 GS-12R (front control panel) Reverberocket II and it sounds great but I need to install a 3 prong AC cord. I have worked on a lot of Fenders and Marshalls and even an oddball amp or two but I can't figure out how to remove the Ampeg's amp chassis...got the back panel off (the clutch-drive screws didn't deter me). WTF?. No screws or straps, etc. What's the trick to pulling the chassis out?