Hot-set rivets are best, Allen-head shoulder bolts in reamed holes are next and Grade 8 bolts with smooth shanks would be my last choice. Use SAE flat washers on both sides and red Loctite instead of lock washers if you choose to bolt it back on, after drilling the holes to make sure they're as round as possible, with the part clamped tightly in place while you're drilling.
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!