... they are awesome! If you ever get the chance to play one, don't take a pass. Blues, Country, Funk, Jazz, Metal: the capabilities of these beauties are suited to all styles of music.
There were three versions produced between 1973-1980. The L6-S or L6-S "Custom" is the one with the six-position chicken-head knob and the special series/parallel & in/out of phase wiring.
It came mostly in Black with an Ebony fingerboard and Natural with Maple fingerboard. There were also some in Cherry, Wine Red, Tobacco Burst & Silver Burst. Total production was upwards of 12,000.
Here's a couple for instances. These demos are pretty decent for explaining the pups and controls but he doesn't quite do it justice.
http://www.youtube.com/watch?v=1SDWWSY6XTk http://www.youtube.com/watch?v=kmOeu1PJslI