Didn't want to pollute the qav400 thread so I'll post here.
Here's how I've installed my G3 on my QAV400. Takes 2 sec to remove the gimball from the qav400, no need to mess with screws, simply unplug the power from gimball, pull the tubes out and voilà!
Cannot wait to try it...won't be today since it is -16 Celsius with wind factor here today