"OK"...found it; GUITAR PLAYER mag, May '89(Hendrix cover)has a feature on Jimmy Johnson.
First question-
GP-"You were among the first 5-string bassists.
JJ-"Yeah, I got my first one in '76; unfortunately, it was stolen out of Alan Holdsworth's truck a year-and-a-half ago. Anyway, the idea came from my dad, because all the orchestral basses have extensions that allow you to go down to low C.
...so I got in touch with Alembic, who was making 5-string basses, but with the high string on top, rather than the low one. Nobody had asked for a low B. I got in touch with GHS & asked for their largest gauge; it was basically a huge E string a .120. I'm using .125 now. Some guys use really huge ones, like a .140."
BTW-
Don't forget Fender was already making a 5-string bass; Jamerson even played one(though very, very briefly as it sez in STANDING IN THE SHADOWS OF MOTOWN).