What I've understood, getting the picture out of Lynx or Game Gear is a bit of a challenge. Controls and sounds should be relatively easy, though. Of course, something like PSP would be simple, with build-in tv-out. Perhaps rig some wifi-controllers, put it all in an old NES-box (which you've gutted for a portable), and viola!
I've had this brainbug of getting the innards out of a Gamegear, and inserting them into an old slide projector, the LCD where the slides go... Huge screen GG.
![Wink :wink:](./images/smilies/icon_wink.gif)
Of course, one might only need a lamp of sufficient luminosity, and perhaps a bit of optics.