Measure and mark the center of each 1-by-1-by-3-inch block on one 1-by-3-inch side using a tape measure and pencil.
Drill a 3/8-inch diameter hole through the center of each block on a drill press using a 3/8-inch drill bit. These are the latch bolt holes.
Turn the blocks so that the hole is oriented horizontally. Drill a 1/8-inch hole, 1-inch in from each end in the center of each block using a 1/8-inch drill bit. These are the mounting holes.
Align one block with the mounting holes facing outward against the operating edge of the door at the height you would like to locate the latch. Drive a wood screw through each hole into the door with a screwdriver. Align the second block with the mounting holes facing outward against the edge of the door opening directly across from the first block. Hold a level across the top of the two blocks and adjust the second block until it is level. Drive a wood screw through each mounting hole into the side of the door opening.
Place the dowel on a work surface. Screw the knob into the center of one end of the dowel by turning the attached threaded screw clockwise until the knob is tight against the dowel. This is the latch bolt.
Slide the latch bolt through the 3/8-inch holes in the blocks to secure the door. Grasp the knob and pull the latch bolt out to release the door.