Thanks for the replies, I put a case in with Ag Leader regarding the same questions and they said the SF3 signal will work and also that it would likely use the JD Magnetic north lines.  However I tend to agree with you, I believe it follow the True North lines generated in the Incommand 1200 and Z2 controller.  I did test this out this morning going nearly straight north 1.72 degree heading and for a full half mile where I could see my tracks in the dirt.  Lined up directly with the fence post at each end corner that I had set last year with a full Ag Leader system (GPS7500 on RTK).  From one end to the other using the SF3 with everything else Ag Leader, it was spot on (or so close that I couldn't tell).  I feel I'm good to go.  Thanks guys