It's basically 2 modified well known circuits in series (TubeScreamer & Shredmaster).
There are 2 versions:
- a true bypass version were you wire two separate 3PDT footswitches in series.
- the original Visual Sound version which uses a Multiplexer Switching daughterboard.
The result should be a much smaller pedal compared to the original.
You can check Strassercaster verified version on the forum section.
Schematic and original thread from FSB are available here.