If you still want to relive your Atari 2600 game playing days and simply modding your Atari 2600 controller isn’t enough then why not bring back the entire console by hacking it into a new form factor and use a new LCD screen on it? That is exactly what Kyo did, have a look at all the build details here.

"It is true, you have heard me. I am making an Atari Jr. 2600 (PAL) portable Why? -I had a board available -I’m using a PSOne screen anyway, so it can be a little bigger without contributing to additional size but most of all, -Challenge"