The Ramcharger I once had, was similar to yours. Had the double cardon at the transfer case, down to the 1410 u-joint at the D70. I had the 6" springs, but no block. The D70 was set at 3° down, but I had changed my rear shackle to be in compression, not tension. That rotated the D70 to get that angle. I never was over 50mph with that truck, as it was more off-road than on-road, but never noticed driveline vibration. With your welded block and 5.13's your going to be twisting the diff, more than mine (4.56's with 42's). Loads of leverage there.
My current project will be 1° down, but I welded up a traction bar from an Off-road Design kit - hopefully no D70 rotation. Might be something to look into...