Here's another Dragonfly design. This one is basically two tweaked Electra Distortion circuits stacked back to back. Here's a sound sample. Should fit pretty easily in a 1590a.
This is a library of perfboard and single-sided PCB effect layouts for guitar and bass. I'm not an electrical engineer by any stretch of the imagination, just a DIY'er who likes drawing layouts. It is meant for the hobbyist (so commercial use of any of these layout is not allowed without permission) and as a way to give back to the online DIY community.