Obviously an interesting card. A few rules I'm trying to clarify here, all regarding fetching an equipment as an instant for some other attacking creature.
Note Stonehewer Giant is not attacking here.
1) After declare blockers step (say defending player said no block), and before damage, can you use the Stonehewer Giant's ability to go fetch a Worldslayer to blow everything up, without a chance for defending player to announce blocks?
2) After declare blockers step, say defending player has announced blocking with a black creature, can you then to use the ability of Stonehewer to go fetch, Sword of Feast and Famine (give protection from black), and completely void the blocker?
and 3) After you announce attacks, and they announce a blocker, can you then use Stonehewer to go fetch Argentum Armor and have its ability trigger? Basically after the blocker is announced, and if I then attach Argentum Armor to the attacking creature as an instant, does the ability trigger (Whenever equipped creature attacks, destroy target permanent.)?