Thanks! I will try powering the gameboy with 5V today. Also I found this video when looking for the mounting options:
EDIT: The original stripboard had a mistake!! The 1k resistor should go to the lower left pin of the LTC1799 (pin 4)!!
(from this video)
That looks like a voltage mixer to me! I will go with that!
Edit: I found more info in the zine!