The only bass/guitar doubleneck I've actually witnessed played live was this homemade job in this weird arty underground band Spongehead back in the late 80s.
Can't see it very well in the lo-fi video but:
Funny thing about this band, when he was playing the guitar neck the "bass" role was filled by his brother - as on this tune - playing baritone sax through an octave pedal through a bass amp. That sax sounded pretty cool.
