All frame dimensions are in millimeters.  Most dimensions are from center of frame indexing holes.

When I did the installation on my frame, I first marked the centerline of the old solid axle on the top of the frame rails.  I located the new suspension in the same location (fore and aft) as the old one and raised it so that the ends of the batwing were centered in the frame and the batwing mounting bolts were in the correct position vertically (dimensions R3 and R5 in picture 1 and R1 in picture 2).  Before welding any of the brackets into place make sure that the new axles are "square" with the frame centerline. Don't expect these dimensions to all line up perfectly.