I have read that he normally tuned the strings to the usual pitch, and as you say in unison except that the upper (as the guitar is held) string in fifth and sixth course were tuned an octave higher than the lower ones to make the bass ring more.

He only tuned down when the strings or the guitar were showing signs of wear to preserve them a bit longer.

My source for this will be found in the thread TWELVE-STRING GUITARS which might have some other material of interest to you.

I don't know what guage strings he used. That would be interesting. I'll bet they were the heaviest he could find. Reports of people who heard him live are that the instrument in his hand was LOUD.

Murray