I can have a crack at this sometime in the next couple of days if no one beats me to it. Those diodes are nothing special, just low Vf Schottkys, could just as easily be replaced with 1N5817s; they are part of the charge pump circuit.
Here you go! As always, give it a look over compared to the schematic before building it. I've been away from the game for a while so there might be some mistakes. I've not bothered to lay out the power supply section; it's very much overbuilt for the application, and you can use the 18v charge pump circuit available elsewhere on this site to feed the circuit. There's also no need to use a 3PDT for the mid bypass switch so I've just laid it out for a DPDT. You can use a center-detent pot for the mid control as they indicate, but a regular one should work fine as well.
Apologies in advance for any image quality issues, I've just started using the new version of DIYLC and I'm not 100% fluent with it yet.