tomrxy, In my experience, yes. Ones I've done need the right size 'tap' so better to have a few and expect to drill in stages or different bit diametres until you find the right combination and it works. You can guage the approx. dia. by one of the existing bolts and the size of the Allen key that fits. Start small and get bigger as necessary.
I pressume the engine bars came with new (longer) bolts anyway? My Heed bars did.
HTH

Oh yes, as RN says, one side at a time only!