It's basically a Rams Head Muff with an added Baxandall tone control.
You can find original FSB thread and schematic here.
It should easily fit it in 1590B size box.
Crank
both treble and bass and you get a classic scooped midrange. Back both
off, while turning up the volume knob and your midrange content
increases. Park the treble and roll back the bass and the midrange scoop
frequency shifts downward so you have complete control over which
frequencies you are cutting. Roll the bass below noon and you start to
add a bump to your midrange, which is great for running into a hot amp.
This tone control style is capable of numerous sounds, making the Manx
Loaghtan one of the most versatile pedals of this style.” - See more at:
http://tonereport.com/blogs/lifestyle/big-muff-shootout/page/three#sthash.Pt8yzCYp.dpuf
Baxandall tone control
Rams Head Muff
Rams Head Muff
Rams Head Muff
Rams Head Muff
