Mine has the long portion of thread sticking out.
I will forward this to ex-wife # 1 , she thinks she knows something about stud's
I would go with 12.9 grade stud and locktiteGB
I wonder though if a 10.9 would be overdoing it threading into aluminum? Probably no more than an 8.8 I guess, just thinking out loud.
Torque spec on that 13mm nut is not that much mind you... I think you'll be fine with what you've got.