Even if you will build both channels I think the input stages in each channel could be used.
You eliminates some channel switches and you can use them as two separate preamps for 
instance. 
                                                                                           

The signal passes through the input stage with ca 2 times amplifying and some frequency 
boost. Then you can select either clean or "dirty" sound in the next stages. The red LEDs in
the crunch part give a slightly clipped tone which is good for rhythm. I am sure germanium 
diodes will work as well. The latter types of diodes give, according to me, the most musical 
overtones when you use the clipping technic. After the preamplifying comes the tone controls,
or "EQ", as I call it. I have chosen the OP-amp IC type LF351 because it makes the tone a 
little softer than TL071, I think, and it works well for rhythm sounds. An
important thing is that I have listened through a Celestion 12" speaker that has its special
sound. Therefore the component values in the EQ might be modifyed, especially the middle 
control.
                                                                                               

If you build both channels you can lead the signal from the master control to a mixer and 
perhaps to a reverb driver.
                                                                                          

The voltage should be about +-15V to get the cleanest sound.