I think the amp has better head room for high output guitar pickups and better overall balance in the tone, when I attenuate the bass a little and remove the treble boost. This means making C3 1000pF instead of 1uF and eliminating R29 and C30. The  schematic below reflects these changes.

New schematic with minor changes in values:

https://circuitsaladdotcom.files.wordpress.com/2013/03/portaamp3a.gif

Fortunately the layout remains the unchanged!

Gain distribution is tricky in this amp, partly because of the low voltage supply and the need to not over drive the FV-1.  Some may have trouble with the first preamp being overloaded with hot signals. Increasing the emitter resistor R5 in the first stage and lowering it in the last R24 may help with this. The overall point here is that there is lots of room for adjustment.