Sounds like you have the right idea.
If you ever have any questions about pinion angle and driveshafts they will be answered here, I suggest you skim through the entire thing, and read the part that looks like your setup.
http://www.roadranger.com/Roadrange...=Installation%20Guide&Language=en_US For your setup you will need the pinion centerline and engine / transmission centerline to be parallel.
You can't talk about the pinion angle without also knowing the engine centerline angle. It is the relationship between these two angles that is key, one without the other means nothing. However if the u-joint angles get large you have a problem, but in a stock situation this won't happen. Read the Spicer manual so you understand how u-joints and driveshafts work...
To center the rear I would first center the ends of the trailing arm brackets on the axle by measuring from a machined surface at the end of the axle tube on each side. Usually the backside of the flange the backing plate bolts to is machined, or check to see that that flange is the same thickness both sides and you can still measure from it if it is not machined.
While trying to make the left and right side measurements the same make the center of bracket to center of bracket the same measurement as the original was.
Once that is tacked in place, and even finished welded you can center the rear axle in the frame by adjusting the location or length of the panhard bar. I would drop a straight edge down both sides of the frame and make the distance from frame to backing plate on both sides the same at ride height.
The location of the bed, fenders, and tire all have a pretty slack tolerances. You need to pull all measurements from accurate preferably machined surfaces and the frame.
Grigg
