This is verified, I did make a few changes. Per Frank_NH in this thread:
http://guitar-fx-layouts.42897.x6.nabble.com/Mammoth-Electronics-Nuclear-Winter-Distortion-td42541.html-Replaced the 470k resistor from the gate of the J201 with a 1M resistor to ground
-Replaced the 6.8k resistor from the drain with a 22k resistor to bias the J201. Voltage gain ended up being around 7.5V, so a trimmer might work better here.
-Gain pot is backwards, should be 1&2 to ground, lug 3 to the 1K resistor (I used 2.2k here, which is what my schematic from Mammoth showed).
Sounds ok, gain is bunchy right at the end. Frank's suggestions solved the volume issues I was having with the original PCB that I bought from Mammoth (that I scrapped).