Basicaly, depends on your wishes.
Building a showcar or period correct racecar.
From all the GT40's I photographed at the international historic races (Netherlands, Belgium, UK, France, Germany) I visited the last 5 years (to get a reference for my build).
Non of the gaps are the same or equal, not even on the same GT40.
Not even the fittings of the top of the doors.
My paintshop wanted 1/4 atleast as the fibreglass body will deform in the sun.