I belong to a vintage Kenmore group on Yahoo, and here's what they say:
158.500 1960-61; 158.501 ‘61-62; 158.502 ’61; 158.503 ’62; 158.504 ’63-65; no year shown for 158.505.
Your specific model number should be on a plate on the machine. Sorry, I don't know where it is on yours. On my 1974 model it's on the front when you tilt the machine up a bit.