I'm pretty sure he tuned down a full tone to get that stretch across the fretboard Mark, still.....he was a good one.
More SRV trivia: The frets on his main guitar were bass gauge fretwire. I got an old squire bullet that I refretted the same way for the hell of it and they are not a bad thing at all! Will keep you from flyin' clear off the neck;~)

Yerz,
Tweed