This is about as far as we got on our Inventor design yesterday.
The black shaft is driven by the motor/gearbox. The pink spool has bushings which allow it to rotate and slide on the shaft. The light gray pin is pressed into the black shaft, it turns with it.
Not shown is the "fork" and it's actuating pneumatic cylinder. The fork fits into the groove at the left end of the spool, and slides the spool along the black shaft to allow the two pins on the end of the spool to engage or disengage the other pin.
To wind the winch, the spool is slid by the cylinder/fork to the right to engage the pins, then the motor runs, then stops. The cylinder is energized the other way to disengage the pins, pulling the spool to the left, and allowing the winch to unwind suddenly.
This still in the design/fabrication stage, if you see any problems, please let us know!