Well, spent the morning with the circuit again. I managed to get good, full-volume sound with the bass boost, but to my ear the boost did very little (if anything). The cap from +V to ground seemed to kill the oscillation, which is excellent.
I also tried a few different values for the capacitor that connects to the volume pot, and found one that works (or sounds) much better than the suggested value.
All in all I'm pretty happy with it. It loses distortion/sustain on both the first and sixth strings, but not enough to be problematic (it's only noticeable if you're hitting strings and letting them ring out)
Will solder it up in the next day or two, and drill an enclosure. A while ago I ordered some cool 30 x 15mm black hifi knobs which might be just the ticket for this pedal