Welcome to the forum Perhenric! And thank you for the extra information.
It is good to see the gas turbines can be converted to run on LNG - gas turbines being remarkably flexible with other fuels besides kerosene and what you wouldn't think would be fuels in certain applications, with what the Abrams Tank has been run on coming to mind in that regard!
The LNG storage would be the problem as you mention, however another member of the forum going by the username HolyNougat used to work on QM2 as a deck officer and said she has a lot of spare "dead" space behind the scenes, the most he's known on any ship and particularly compared to QE2. Maybe this would be in QM2's favour?