I never built it, but I like the idea to build it and add an easy eq in my DIY 1590A pedal collection.
You can find the original layout in this document http://runoffgroove.com/MrEQ-layouts.pdf.
It's not small enough. So I tried to redesign it.
It's just a bit modified, so it could work, but I signed it still as unverified.
I'm not 100% sure if it fits into a 1590A box. The board is a bit longer, so the input and output jack should be mounted as close as possible to the top of the box, and put the board over it without hinder the board. I never do it, but someone does.
Probably the board should be placed over the three toggle switches, we don't have much alternative. So we should isolated the three switches from the board we place on it.
And the parts on the board have to be more low profile possibile. I advice to use box film caps.
The 220uF could be a problem, the only thing to do is, I guess, to use a 11mm lenght one and bend over. The ground wire could start from any other spot from the ground track.
Another trick to earn a bit of room is to leave off the inner nut of the switches. It will be a bit more out from the box, but maybe I wanted to use the ones with short lever.
I can't build it soon, but let us to know if someone want to try it.