I modded mine using this tutorial: http://www.instructables.com/id/Sega-Genesis-Model-1-Region-Modification/ however it only works for US/JP games, because I did not mod the crystal to play the PAL games. It's enough for me, though.
Regards.
Oh, shoot. Right, these are different and do not have the serial port on the back. Also, IIRC, these are the ones that do not have good sound. I think you are better getting a nicer HDG Genesis (should be about $10-$15 console only) and maybe selling/giving away this one. It will be better sounding and easier to mod. Anyway, this russinan seems to know how to mod your Genny: http://www.emu-land.net/forum/index.php?topic=56804.0
Regards.