I'm still chasing my vibration issues. I found some pretty good stuff online regarding getting the angles right, here's one
http://www.hotrodhotline.com/md/html/drive_shaft_harmonics.php
though every article I've found assumes a live rear axle whose pinion angle naturally changes as a reaction to the tire torque. We can set our angles exactly as our diffs shouldn't rotate upward under torque like a live axle would.
Some sites are adamant about measuring the angle directly at the U-joint caps to get a consistent machined surface, this can be done using the right size socket as a spacer.
I found some slop in the front u-joints of my nearly new driveshaft, and also discovered the bolt head clearance notches in the forward diff crossmember were not made big enough so the bolt heads were directly transmitting noise to the crossmember. I'm really hoping these two things are my answer,and then the only other issue is excessive lash through the R200 and/or halfshafts.
I'm also going back to factory style rubber mounts for the mustache bar and am testing a factory Camaro rubber mount for the front of the diff. MIne's a street car and the diff howling is maddening. I'll document here if this quiets things down well.