Ok. As far as GQ stuff goes, it all sux !!! HAHA, no not really.
Putting Q tank in GU is do-able but not advisable.
Because GU's have more gear underneath, ( the extra fuel filter pump thingy) it is difficult to make Q fit. Hoses are on the wrong sides, and different sizes.
So the moral of the story IS
do not fit GQ sub tank into a GU, unless you want a excessively huge headache.
In the end, I did not do it, and am now hunting for a GU LR sub tank. Soooooo, if anyone knows of a 2nd hand subby for a GU, I want it.