The bolts fit into the notches provided in the pulley brackets.  This keeps the belt tensioner compressed so you can remove and reinstall the belt without damaging the tensioner.

Note that it's made of angle iron.  I originally used flat steel, but it just wasn't strong enough.

94 and later use 4 1/2" spacing; my '91 required approximately 5 1/8" spacing, which is what's shown here.