It's probably important to note that Brain Stew's guitar/bass isn't diatonic, though. If you're trying to make a mashup or something using it it won't necessarily work, the vocals are what let us call it G# minor rather than some obscure scale (blues octatonic minor?) involving G#, C, C#, D#, E, F, and F#. Without the vocals those are all that's there, with them we get an idea of the important notes which allows us to analyze the F and C as accidentals. The vocals of Brain Stew have a G# coinciding with the F power chord, which is consonant, but in other songs it could just as easily end up a B, which would form a tritone and minor second.
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Before Rockband ever came out there were a few acapellas and instrumentals floating around, notably I remember having them for Brain Stew. Does anyone know where these came from? I'm pretty sure they weren't done artificially but I was younger then and can't find them now because Rockband so maybe they were.