The Marshall Guv'nor is one of the more highly regarded overdrive/distortion pedals of the late 80s, early 90s. With it's amp-like dynamics and a wide range of versatile tones, the Mk. I version of this pedal is still highly sought after. Many artists have used it, though Gary Moore is most associated with it, thanks to his "Still Got the Blues" album.
You can use right angle PCB pots, mounted from the solder-side of the board if you like. It should fit nicely in a 1590B.