Interesting stickers on it, the one with the faded red "WARNING" text also reads: "BOEING LIMITED PROPRIETARY information must be properly controlled."
Looks great! I agree with fohat, the ANSI enter/backslash and backspace mod is well worth doing for the 2u backspace and does not require any non reversible modifications.
Regarding the addition of Alt keys, the Dremel work can also be done on the caps instead of the case. I'd have to double check, but using 1.25 ISO left shift sized keys might also fit decently and wouldn't require any changes to the case or caps.