The changes in the gb_styles.css is ok.
I don't like the changes in the gridview style where you simply removed left alignment, you should re-submit that with something that only affects rtl.
Also for the 2 skins, I am not just replacing those files, you need to only send me the files that changed and you need to make it easy for me to find your changes in the CSS files by putting comments near them, ideally putting all your changes near the bottom of the css file(s). I see the small changes in layout.master, those are ok, I got them.
All of your css changes should be specific to rtl by having html[dir='rtl'] as part of the selector in css to override the default style rule, no changes for ltr should result. (please include the quotes html[dir='rtl']).