Ok guys, this is my first post here at XDA.
For the guys who asked how to change the power buttons and the volume rockers, it's very easy: The two parts are fixed on the mid-plate, so, unscrew the mid-plate and see who they are fixed. Sadly I can't post photos yet because I don't have received my SGS yet. (It's used with cracked screen, but was cheap.)
But I have changed the LCD from my sister's SGS+ (I've used the SGS one and it worked!) and it's very easy (assume if you buy the whole LCD, pre-assembled with digitizer and the chrome bezel.
And I've found at eBay the front screen with bezel at eBay for 105 US$. The seller claims it is original, but never know...