This guy did a good job with it. Same concept... kinda. He used all CMOS 4000 logic chips instead of the 555. http://www.jacobwatters.com/c-monster.php
I've started work on a similar project. It'll probably be a while before it gets done though. I'll try to post results when I'm finished. I want it to be polyphonic, so I'm looking at building an osc. for each key using the 40106 IC (6 osc. per chip). Probably 36 keys.