Here's another one I was surprised I hadn't drawn up before. Like the Custom Badass '78 Distortion, it's also based on an old Boss pedal—the SD-1. (Or I guess you could say it's a modified version of the Zakk Wylde Overdrive, but that's based on the SD-1... Either way, it's definitely been modified with the added 100Hz control and the Bump switch. Here's the schematic for reference. Should fit nicely in a 1590B.