I think that the Fuzzrocious Grey Staches are GGG Tuned Muffs,..if that gives you any indication.
The Muff Circuit is pretty straight forward.
I've successfully built the GGG CB1 (EHX LPB-1 clone), the only issue being that the LED was omitted from the kit,...so I had to source one from Radio Shack.
I really don't care for the 125B enclosures they provide with the kits,...they are a little crude and require quite a bit of clean up to make them look nice. The 1590BB enclosure may be a little nicer out of the box and require less time at the sander/grinder but I honestly have no experience with them and I don't know if they are 4site (or other brand) or if they are actually Hammond enclosures. Be aware that the 1590BB enclosures are bigger than the 125Bs (closer to the actual size of an EHX Big Muff).
EDIT: Just to give you an idea. This is the 125B enclosure out of the box.
The right side edge (depicted as the top as oriented in the photograph) was rounded (bullnosed?) over while the left side edge was ground at a sharp angle. You can also see that the bottom plate protrudes out past the wall of the enclosure,...very messy.
After hours of sanding and clean up I was able to get it looking nice.
Note that the bottom pic was not the final product,...with access to power tools I was able to bullnose the sharp edge and get the bottom plate to line up more cleanly with the walls of the the enclosure.
This may not be of much concern to you,...but I wanted something clean so I could work on my aesthetic cause eventually I intend to be building and potentially selling scratch built pedals.