I would.
9.8 is overkill for that. (Maybe they were counting on people not torquing them correctly in the future, and having what happened here?)
Grade 8, 1/2-13 bolts will work fine. With nylocks so whatever you torque it to, it won't rattle itself out.
My understanding was 8.8 is equivalent to SAE GR2 and 9.8 GR5 with 10.8 being equivalent to grade 8. I could be mistaken though.
I would be happy with grade 5 SAE bolts. Not up to ***** on metric stuff really, don't care to be honestly