Could you be more precise as to in what way the jaws are currently 'out of true'? Not perpendicular to the vice base? Not closing parallel viewed from the side? Not closing parallel viewed from above? Or jaws just dinged up from use?

Depending on the issue, other non-grinding solutions may be possible/easier...

Normally, assuming the mounting surfaces on the vice are good, you'd just make up a new set of jaws from ground flat plate (or aluminium plate, for soft jaws) and bolt them on in place of the old ones.