Just a FYI, grade 8 is not more brittle. It is stronger, and does have less ductility which is the amount of plastic deformation (permanent stretch) that occurs between yield and ultimate failure. But the shear strength, which is proportional to tensile, is higher for grade 8 vs grade 5, for the same size bolt. Grade 8 is heat treated after cold forming to give the strength, whereas grade 5 is just stronger due to cold forming. The ductility is not brittleness, they're different properties that are sometimes used as interchagable but should not be.
Just some info from a metallurgical engr (me). I would use grade 8 for that application.
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2005 Kenworth Showhauler 45 ft total length
twin screw, 450 hp ISX, 10 speed Ultrashift
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