I just worked on some of those shifters today and yes, the key is removing the cable and barrel adjuster, if so equipped. Use a dental pick to get the pawls moving. A drop of penetrating oil sometimes works better than WD.
By the way, it looks like the front canti yoke may be too high for good braking. If the front brake is weak, lower the yoke (let cable out) and extend the shoes in. See Sheldon Brown's article on cantis for clarification.
Are you sure the missing chain ring teeth aren't shifting aids? Those often look like unusual wear.