It's the one Buddy had made after he had the basket weave single neck. I think the double was too heavy, I'll ask him and see.
The two bridge pickups acted as a humbucker and could be out of phase, (sort of Strat like.)
The third pickup on the nut end was so that when you turn on the pickup, play in E at the 12th fret and slide down, the notes coming out would go both up and down.
(Another one of Buddy's incredible ideas.) There's a couple places that he used the 3rd pickup on a session, (of course I can't remember where.) It's an amazing sound. Sort of like playing the unison 2nd string C# and the 5th pedal C# and playing that Half a Mind type lick, only the bend could last an octave. One of those things you think is overdubbed, but Buddy did it all at once.
I remember Johnny coming into the Steel Guitar Emporium and we'd set for hours and talk steel. He was an incredible guy. I always told him I wanted to buy this guitar from him, (even thought I'd have no idea where to start with a 12 string E9 or C6. Doubt my back would like it much, either.)
Thanks for posting the pictures! Seeing the guitar brings back a lot of good memories.