Got a request for this one, and it's an interesting Big Muff variant. If you're a fan of Muse you're probably already familiar with this one. There's a germanium input stage followed by a fairly standard Big Muff circuit. Here's the schematic for reference. It would be a tight squeeze in a 1590B even if you wired the pots off board, but probably doable. Otherwise it should fit nicely in a 125B with top mounted jacks.