The publications at the time refer to it as a Gee fix, so this ‘Gee Box Fix’ is probably just used to summarize the log at that point.

Depending how the cookie was armed, they probably weren’t able to drop it ‘safe’ either even if they had they reached 6000ft.
On one mission that G-George (W4783) 460 Sqn RAAF flew, they were over the target at 6000ft and dropped their 4000lb bomb and it buffeted the aircraft so much that it popped out one of escape hatches.
I’ve also read of a ditching where they dropped one at 4,500ft which must have been pretty bad.

The chart you’ve posted is also the Navigators plotting map which shows all his workings such as fixes, wind and air and ground positions etc.
A Gee chart or lattice chart would typically be in 3 different colours and have arcs coming out of the various stations, like ripples in a pond.

Thanks for posting the information.