[OG68]

The FM Stereo has push buttons that are labeled AM - FM on the ends. The FM Mono has a selector dial behind the tuning knob labeled AM-FM
IIRC the B body AM-FM has a heatsink is mounted to the side of the radio. The A body AM-FM has the heat sink mounted to the back of the radio, This is done to clear the heater controls on the 68 A body.