I have all of the parts to build one of these (BSIAB-II) but haven't gotten around to it yet. I have a few pedals to complete this week but I think I'm going to put one together after that. I've been curious abouot this circuit for sometime.
You might also like to look at the Jetter Gain Stage Purple. I'm not sure if it's exactly the tone you're after, but it has less gain than the Crunch Box and is still very Marshally, great sounding pedal.