Well shit, guess the Fisherman's Fuzz couldn't survive the rehearsal space floor or maybe was doomed from the start... I got home from there (where it had worked but below unity volume) and hooked it up, noticed a volume loss situation that seemed to get worse/quieter the longer the circuit was on.
Not stoked on going over the Millennium bypass or rewiring the switch again, I replaced the circuit with an identical but smaller one I had built in parallel, and a neater, separate pot/3PDT toggle switch solution. NOW it fucking works and can be handed over to my bud. I still don't know what exactly went wrong with the mk1, may or may not try the MBP switching method again. Is is really worth it just to have a pot/switch combo with LED indication.