This might be a little long-winded, but....Forget the driveshaft angle... On our cars what counts is the angle of the centerline of the transmission output shaft, in relation to the rear pinion. Pinion *should* be somewhere between 3 and 5 degrees down (and opposite) from the trans angle, on a (leaf spring) car with the suspension at rest. I know this gets debated (argued?) a lot but this is the right way. It's how the factory figured it as well.
For example... if the trans is pointing down 1 degree, aim to get the pinion pointing down 2-3 degrees. It's like the positive-to-negative number line in math class....If the pinion is down 2 degrees, and it moves up 3 while cruising, that puts it 1 degree up, which is the same angle as the trans being 1 degree down (=parallel angles). It does always move around, so a "close" estimate to parallel while driving is good enough in this case.
You just don't want it to be near parallel at rest with a down-angle on the trans..or worse, pinion pointing up at rest...
And I know you know your stuff....but as an option to getting confused by the "this is how I do it and it works fine" internet crowd, you could give Cass Eslick (the Dr. of Diffs) a call...he'll help you get it right without the noise.