level 85 gear 8 both needing the last final piece to go to gear 9
This. I was only level 80 (having a credit crunch) but was in exactly the same place on gear, so those last 5 levels probably didn't mean much.
@Ruyen
Since both @theanswer3 and I eventually completed it at that gear, I would imagine that if you get Luke to g9 it will be even easier.
Took about 12 total attempts for me, including 4 or 5 when I was just doing my first two attacks, seeing if they kill Scout, then starting over hoping to get both Luke & STH to crit in the same effort.
So even after you get g9 you'll still probably have to try more than once, but you should be able to do it if you try a few times.