You should find your meter impedance from the make and model basically you want a 10M ohm impedance for accurate readings
BIAS: Controls the filter resonance frequency. When Sensitivity is turned fully off the Bias can be used as a sweepable filter.
There’s some information here on the old site which runs through the circuit with the block diagram (below)
If you click on a link that doesn’t work just add .webs to the url eg guitarpcb.webs.com
I wouldn’t give up with this pcb you can always bypass traces if pads are lifted by connecting components directly with jumpers as you have with Q1 the pads are also double sided so you can solder component side also if needed