With the Kingslayer you could do a diode lift just by using an on-off-on switch, but without the clipping diodes I would assume you would get no distortion because I don't think the op amp would clip on its own, if it does it would be very minor and you would just probably be boosting volume. You could increase gain by making R10 larger and making R8 smaller. But, I think it would also lose some thickness in the tone, so you would have to mod other parts to compensate, probably increasing C7, maybe C6 to let more bass through.