Did you already try to add a custom aspect ratio (yours 5:3)?
(rightclick >) Options > Preferences > Video > [General]
You can add "Custom aspect ratios" in the "grey" area at the bottom, by typing in the desired ratio in the small white box and then click on [Add] (so that it is added to the list in the larger white box).
If you have added a ratio, it is shown and can be selected under
(richtclick >) Video > Aspect ratio
(the added custom ratio will be shown below the predefined ratios)
-offtopic-
:
You can select what you want to be displayed when depressing [i] under:
(rightclick >) Options > Preferences > Video > [OSD Options]
(in Dutch "Keuze schermmeldingen")
