There are three steps required to get the layout partially^[NB!] right:

1. Change 3rd level chooser and switch Alt / Win (cmd) key.
2. Edit the XKB-file to get keys right.
3. Set the keyboard in  Ubuntu to “Norway Macintosh”

Step 1:

Open the keyboard settings (System -> Preferences -> Keyboard) and click the “Layouts” tab. Then click the “Other options…” button.

1.1) Press “Alt/Win key behavior” and choose “Left Alt is swapped with left Win-key”.
1.2) Press “Third level choosers” and select “Press any of Alt keys to choose 3rd level” (or “Press left Alt keys to choose 3rd level”).

Step 2:

This part is a bit more tricky.

Open the terminal and open the folder “/usr/share/X11/xkb/symbols”

$ cd /usr/share/X11/xkb/symbols

The file we are going to edit is named “no”, but before we begin lets backup the file!
From now on every command run as root (noted by #).

# cp no no_backup

Now open the “no”-file with your favorite editor, I’m using VIM.

# vim no

Scroll down to the part which starts with:

// Copied from macintosh_vndr/no
partial alphanumeric_keys
xkb_symbols "mac" {

You now need to change the following lines:

key <TLDE>  { [      bar,    section, brokenbar, paragraph    ] };
to:
key <TLDE>  { [      apostrophe, paragraph, bar, brokenbar ] };

And:

key <AE04>    { [         4,  currency,       dollar,       dollar ]    };
to:
key <AE04>    { [         4,   dollar,       currency,       dollar ]    };

Then save.

Step 3:

The only thing remaining is to select “Norwegian Macintosh” as your default keyboard layout.
In System -> Preferences -> Keyboard, press the “Layouts”-tab and press the “+”-button.

If everything is done right you should have the basic Norwegian mac layout.

NB!

This layout is not equivalent to the real Norwegian mac layout. There is a lot of keys that needs mapping to do so. The original layout looks like this (keys are pressed from left to right).

Edit:

It seems that if you use the newer versions of Apple’s keyboard you have to change the setup for the TLDE-key and the LSGT-key. I don’t know why, but it works!