Dan, with the DRB using the live rear axle you need to get the drive line right or you will have problems with the universals.
Here is a site to follow:
http://www.drivetrain.com/driveline_angle_problem.html
I'd recommend getting the output from the box and the input to the diff as parallel as possible. Ideally, the operating angles on each end of the driveshaft should be equal to or within 1 degree of each other, have a 3 degree maximum operating angle, and have at least 1/2 of a degree continuous operating angle.
The problem with live axle cobras is the very short drive shaft . You don't want to get the situation where you have to set up the rear springing/damping so stiff that your ride quality suffers because of incorrect angle and phasing of the driveshaft.