Punch holes in 4 of the hinge plates as shown with a 7/8" or 1" punch.

Weld one plate with holes, one without holes, and 3 hinges together as shown, with the plates 1 1/8" apart and the hinge centered.

Make sure the side of the hinge that sticks out most is on the top; this way it won't interfere with the hopper metal below when installing the hopper.

Make 3 more of these.