Get your keyboard setup as close as you can with whatever tools seem comfortable (eg gnome settings) and then dump the layout to an XKB file. Now you can make

Get your keyboard setup as close as you can with whatever tools seem comfortable (eg gnome settings) and then dump the layout to an XKB file. Now you can make the tweaks you need, and load them automatically next time with a call to xkb in your .xsession. Linux and GNU and Xorg et al may be heterogenous and weird, but the joy of an open system is that if you want to take it apart and tweak it, you can.