Check the bits are as per diagram, check the back of the PCB with a lamp and magnifying glass. It's easy to connect 2 things together which shouldn't be connected. Some of the connections could do with more solder, perhaps.

Attach guitar and amp, plug in battery and wiggle the volume knob and sustain knobs. It should work, but only on some positions of the sustain knob. Turning the sustain knob up for maximum volume is fine. Dan Armstrong presumably turned the sustain trimpot down to near minimum volume, I can't see any reason for having it just to turn it all the way up.

The original used 2N5457 transistors, these work well. So does the MPF102, which some Radio Shacks have. J201s didn't work well. I replaced the 2.3k resistor with a 10k log pot, I thought that could adjust for differences between FETs, and it did. I got the J201 working well. But the the 2N5457 and MPF102 work "right out of the box". So it's obviously a good idea to use the right part numbers.

Here we have the test environment: