So this turned out to be a doozy of a project for me. First, the final results:
Started out by stripping down the Raspberry Pi, hoping to fit a larger 850 mAh battery in and got everything soldered together:
Came to find out I made some kind of mistake when stripping down the Pi and I couldn't get the Gem to turn on (all my connections checked out but there was a bridge between GND and VBATT that I couldn't resolve). So I wound up removing the Pi from the Gem using a hotair rework station and was pretty bummed when I wound up with this:
Nearly gave up after this but upon closer examination I only had one pad that needed to be rewired (rest were redundant GND pads)! So I carried on and got the Pi to boot! My next speedbump was no sound due to a blown speaker (I checked the resistance before assembly but somehow it got blown during testing / assembly). My solution was to fish out an old iPad speaker I had laying around and replace it with that:
I wouldn't necessarily recommend this approach since it is a bit taller than the included speaker and presses against the LCD more than I'd like. However, the sound is nice and clear so I'm going to leave it.
Finally buttoned everything up and have been pleasantly surprised how enjoyable it is to play so far!
There are a couple things I may do down the road to improve the Gem:
1. Add L/R buttons so Save States and GBA games are available
2. Place an external power switch so I don't need to remove the cap
3. Re-case into a non-translucent case if I can find one with a cap (or paint the one I have to a solid color).
Thanks to Kite for the kit - fun little project and I look forward to more in the future!