YES, it’s like a gate on a swing and I’ve not looked to see if it’s on rubber bushings but regardless any bump on either tire sends energy directly into the stiff shocks. LOVED the drawing you linked to and as you mentioned, all those linkages are bushinged AND it allows probably a couple of inches of horizontal offset before things get translated to the opposite side.
Has me wondering if the existing setup can be helped with a bit of welding. ie cutting off the straight axle from the body mounted arms, welding some square tubing to the axle and welding bushing holders onto the cutoff ends of the body mounted arms.
First, I have to get under there and see if there are rubber bushings holding the “gate” to the body and see what condition they are in.
Another thought is how much it would cost to get the 4 arms off one of the junk 2008 units @Trip is parting out. I can’t weld aluminum but could probably get a local body shop to weld on the extra frame bracket if the existing frame mount is in the same location as the 2008+ years. ie they only added the extra tab to the frame. I’d have to weld all the tabs onto the axle but it’s steel so I can handle that.