The rounded tabs on the top box (where the sides wrap around the front) and the sheet metal handles lead make me think '60s. The Waterloo logo should be a good clue for someone more knowledgeable than me.
Waterloo stamped manufacturing dates on their tool boxes. On top boxes it should be on the horizontal surface of the upper storage compartment, usually toward the left front. On lower boxes it is typically on the floor of the box. Again, usually toward the left front. Use a flashlight and look carefully. The paint sometimes partially obscures the stamp.