Is this just a "feature" of a two piece driveshaft on a live rear axle?

I put a slightly portly friend of mine in the 86 I've been refreshing the last little while last night in the back seat on the way to dinner, and I'll be damned if it didn't have the same little whacka whacka whacka leaving from a stoplight and some odd harmonics at around 50mph or so. I have experienced this on my 745, which a complete suspension and driveshaft rebuild never completely remedied (overload springs helped slightly, raising the rear), and on my long gone and pretty worn 83 GL.

I'm pretty sure it's a pinion angle issue, my next step on the 745 was going to be adjustable torque rods to try and correct it, as shimming the CSB up and down as Volvo suggested (because they knew it was a problem with the design) had only helped slightly.

This 86 for what it's worth, has non-sagging rear springs, good bushings in the rear, a new center bearing and rubber, good u-joints, new motor and trans mounts.
There is no noise in takeoff when unloaded, but there are still some low level harmonics around 48-50mph, which taper off to un-noticable at 58mph. They take a higher speed to taper off when loaded, obviously.

Solid driveshaft? Should I just ship one to Dennys or the like and say "make me a strong skinny as possible one-piece? Give up? Order the adjustable torque rods and try and tweak the pinion angle till it's gone? Stiffer CSB rubber? There is a urethane called window weld I believe that kids use to stiffen up motor mounts and it holds up well, I suspect the same could be applied to the CSB rubber but it seems like a bad idea. Though the volvo pieces are the softest/floppiest center support rubber I've ever seen on a setup like this. Or I'm buying the wrong brand.

This has been one of my top peeves with these cars since I've been involved with them, and was the last straw before getting rid of that 745. It was infuriating to have a wagon with huge storage space in which you couldn't load it up for fear of the driveshaft coming through the floor, and down right embarrassing for a semi-professional mechanic.

Thoughts?