Hi Dave
Awesome! Yes, the 470uF is critical i'm afraid. If a lower value is used the maximum gain will be lower/weaker. It can be omitted (with a link insted) and it will sound about the same, but it will be alot noisier.
Another cirtical part is the 1N34A diode (somehow other kind of diodes makes the circuit oscillate). The second transistor can be either BC549B or a BC550B, as they are basically the same. But you could experiment with other transistors in that position if you don't have any BC549B/BC550B.
The clipping LED's light up very bright in this circuit when playing, so I thought about putting one of both outside for my next build :)
cheers
/ Fredrik
check out my building blog at www.parasitstudio.se