Just Do a direct VGA mod to the gameboy it wont be overly hard...
You can not have come this far and put an emulator in it.
I would love to do it for you but i am located in Australia, and don't have a gameboy to experiment on they are long gone.
You have a pinout so the hard part is done... send it to a convertor just measure the voltages from your gameboy and lower or raise it to the sepcs of the convertor, knowing these things i would say it would be lower. (Best thing about electronics is its all maths
there is a formula for everything )
Find the exact res that gameboy is producing then find a convertor that can do it, if none exist then go find a chip that can do it, build a PCB on EAGLE-CAD print it out on a laser printer then iron it on, drop it in some acid and away you go, however a convertor may need a grounding plate.
When in doubt about things like this it is best to leverage off other-people and this is not an electrical forum.
You have some awesome skills and there would be many people that excel in this space close to you that are on electrical forums. do a short description of what you want to do and pictures of the project, will be an awesome step to learn another skill set.
Maybe start here
http://forum.allaboutcircuits.com/forumdisplay.php?f=3 Awesome project