Level shifting pedal output to 0-5V
from eyeballing the circuit, it should be this: R1 and R2 sets the 0 level of the output so set R1 and R2 so that their junction is 0.75V. This makes 0.75V input correspond to 0V output.

Now set R3 and R4 so that your gain is what you want, which is (5V - 0V) / (4V - 0.75V) = 1.538. Gain = 1 + R4/R3. That should do it. 

Ideally, the gain equation would include R1 and R2 but if you make R3 and R4 way big compared to R1 and R2 (like 30x) then you can ignore the extra terms keep the gain equation simple and it will be 'close enough'.

Hope that helps, -Vince