Lay the 3-foot seat boards parallel to each other on the working surface. Lay the chair seat across them with 1 inch of seat boards sticking out on one side and a foot or so on the other side. Hold the pieces together tightly and flip it upside down. Predrill four holes through each wood board and into the chair cushion. Attach the seat boards to the cushion with wood screws.
Position the back boards parallel to the seat boards, the same distance apart. Set the back rest on top of the boards and flip them over, keeping everything pressed together. Predrill two holes through the back boards and into back rest. Attach them together with wood screws.
Prop up the assembled chair back where a natural position would be in relation to the cushion. Set the hinges on the boards so that one part is on the seat board and one part is on the back board. Mark the location of the hinge screw holes. Predrill each hole and attach the hinges to the boards with 3/4-inch wood screws.
Set the assembled chair to a comfortable angle and insert the stop blocks immediately behind the rear boards, resting on top of the seat board. Mark the locations. Flip the seat over and predrill a hole through the bottom of the seat board and into each stop block. Attach the stop blocks to the seat boards with wood screws. Test to ensure the chair stays upright comfortably and adjust if necessary.