Hi All and Derek,
The bolts are to act as stops and adjusters for the movement of the gear selector claw. They stop any excess movement that would make the selector quadrant throw too far over when your foot gets too excited to be careful with your gear changing! Reducing miss gear changes in a race. You can adjust and get it just right to suit your box, then re-adjust if wear takes place in future.
Seems to work well, so it is a good modification to do.
Cheers,
Alan