Bob Gibson played a Vega 12 string (probably due to contract stipulations for endoresment of "Vega" instruments.) These guitars used the same body as the Harmony Sovereign dreadnaught. No doubt braced differently with a fixed bridge. From the late 60's to ythe end of his career Gibson played 12 string guitars built by Bozo Podunavac, of Chicago, California and of late Florida. Gibson strung his guitar with D'ANGELICO medium gauge strings. These employ a wound octave A string for a really solid bass. Gibson tuned to D and capoed at the second fret.
If anyone knows any more about the Vega 12 strings I'd like to know.