I had this combo in a dodgy self build mattocaster about 15 years ago
I wired the motherbucker coils up in series iirc, and then just had a 3 way switch (as the black Manson appeared to) to select it and the hot p90
The output on the MB was unbelievable but it definitely did the whole OoS thing, especially if you have some sort of Marshall & a fuzz factory.
There are lots of options for the MB but I don't recall any info about Matt using it in any complicated manner other than max output as I'm describing.