If we're talking '70s - it's not that silly stick thing (the name of which escapes me) is it?
Oh fuck it, I'll give the answer. They all played/promoted Alembic basses at some point in their careers. Alembic was actually formed out of the Grateful Dead's roadie guitar technicians.
Have given this a great deal of thought and decided not to contribute to any further Threads for the time being.