Well GM SI says nothing about alignment of the rear stabilizer shaft links, so I am trying to find out if they need to be perpendicular with the ground/control arms?

 

NO LOWER THAN A GRADE 8 OR 10.9 METRIC AND ROLLED THREADS.
OR GO TO YOUR LOCAL AVIATION SHOP AND GET A AVIATION GRADE NUTS AND BOLTS, BRING YOUR OLD ONE'S OR GO TO "ARP" AND FIND SOME THAT WILL FIT.
On my old TA even with grade 8 and larger bolts and nuts they still failed. So I put grade 9 bolts on and no more failures again. And get one of these.

 

Wow, I noticed the driver side rear just sheered off, just the same as the other side. *rolls eyes*...

 

Prothane/Dee Engineering says they use Grade 5 bolts. By contrast Hellwig's rear bolts (which private labels Strano's sway bars) are Grade 5 too, but apparently higher quality metal, fronts are Grade 8.