The Boss SD-1 is like a DS-1 on steroids. The distortion is more aggressive.
I tried several mods on this SD-1 until I finally found some that I liked. It has a Seeing Eye-Dog mod on the inside. There is a new toggle switch for the tone. In one position a filter cap is lifted out. This gives the pedal a bright loud sound, great for punk or No Wave. Putting the switch in the other position gives a darker bassier sound, like a neck pick up sound.
Of course the boring little red LED indicator has been swapped out for a giant bright orange LED.
Here's the inside of the pedal showing the filter cap and toggle switch.
Here's a photo of the modded pedal with the toggle switch for the tone.