How do you mount these brackets?

what^

ummm the the lower bag mount is ON the lower control arm. Minor cutting? That hump that has to be taken out is more than minor my friend.

it's called "torsion bracket kit" because it is for torsion bar suspension trucks, you remove the torsion bar and use the bracketry to mount the bag to the frame and lower arm

so looking at the pic, the L shaped brackets on the right, and the circle cups on top of them go on the lower control arms.(one circle and lbracket per control arm.) as someone said i think most people don't use the L bracket
the other pieces are the upper bracket that gets welded to the frame exactly right above where the circle plates are mounted on the control arm. the triangles are the gussets and the U-shaped pieces are the actual bag mount. the gussets are IMPORTANT don't leave them off. your shit will break off if they are forgotten.
On your frame, you need to ditch your shock and mounts. clean that area (under the upper control arm, above the lower control arm) where the shock used to be. cut/grind/weld/whatever necessary to get a smooth flat pretty framerail to weld on. you may need to trim the brackets and gussets to make them fit a little closer to the frame. weld them up near the top of your frame. add the gussets either above the bracket or below, but make sure the bag doesn't come close to rubbing (remember some bags expand as they have high psi in them)