Well, if you have uninstalled fglrx 8.42.3, you have to remove the fglrx module from /etc/default/linux-restricted-modules-common. This means that your DISABLED_MODULES must be empty (only with the symbols ""). When you had done this, then you'll be able to install the driver included in the gutsy repos with linux-restricted-manager.
Anyway, I've got to install fglrx 8.42.3 following this steps:
1- Uninstall xorg-fglrx-driver and linux-restricted-manager.
2- Set the driver like vesa.
3- Install the driver 8.42.3 running the .run file with sudo.
4- Set the driver like fglrx.
If you have questions about xorg.conf, look at this post:
In this post, it is my xorg.conf.
May be help you this.