Place one of the 32.5-inch 2-by-4s horizontally on the floor. Measure across the width at the left end with a tape measure and make a dot at the halfway mark. Place a side of another 32.5-inch 2-by-4 on top of the one that is already on the floor. Line up the end of the 2-by-4 with the end where the dot was made. Place another 2-by-4 horizontally on the edge of the top 2-by-4 and line up the ends.
Drill a pilot hole through each end of the top 2-by-4 with a power drill. Drill a pilot hole at each side of the one just drilled. Screw a wood screw through each hole with a Phillips screwdriver. Turn the I-block you have made over. Repeat the procedure with the drill and the screws on each end of the top 2-by-4. Repeat this procedure with another 2-by-4 and the left inside top edge of the I-beam.
Place the I-beam horizontally on its side. Butt up an end of one of the the 30-inch 2-by-4s with the inside top edge of the I-beam. Hammer two nails into the end of the 2-by-4 so they penetrate through and go into the center of the I-beam.
Turn the I-beam over. Repeat the procedure to nail the other 30-inch 2-by-4s to the top inside edges in the same manner as was just done.
Empty all of the contents that are inside the bookshelf and place them aside. Measure the height of the bookshelf. Stand the two sawhorses vertically side by side. Move one of them away from the other for half the distance of the measurement that you just measured.
Grip an end of the bookshelf and have an assistant grip the other end. Lift the bookshelf up and place its side on the sawhorses. Adjust the positing of the bookshelf so that there is an equal distance from each end to the sawhorse. Return the content to the bookshelf.