If you go up on the grade of a bolt, also be sure to increase the torque you use to tighten them. Grade 8 bolts tightened to Grade 5 torque specs will back out due to insufficient stretch to keep them tight. Hope you don't strip the threads in the head!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!