the 3PDT switch board (4Site) does not fit as shown in the build docs. The jack locations and the footswitch location are drilled so that the 4Site board needs to be mounted with the numbered leads facing the bottom end of the pedal or else your cable plug will run into the footswitch.
You could, of course, decide to not use the mini PCB for the footswitch and then the problem goes away. Or you can turn it around and it works, but you won't be able to fit a battery in any longer, as the board now blocks the space the battery is supposed to fit in (and it looks like a wiring mess!). For me, that wasn't a big deal since I use plugin power always.
Either way, if Mammoth reads this forum, hopefully they will either fix the build instructions or move the holes so that things fit. There is definitely enough room for them to move the jack holes further towards the top and still have room for the main board to fit. They only need to move about 1/8".
The actual circuit sounds really nice. Different than most others I've tried or built and I have done a lot of both.