Save the HC for another machine or use it on the one it's on.
The HCs only fit machines with a motor 'boss' that lines up. I tried to fit one yesterday - it was a no go. I hate to scrap out that machine - the motor mounts odd - wiring is shot plus what ever wires are missing plug into the box the machine sits in. I can't remember the name of my machine. It looks sort of like a clone but it is not really a clone. The motor is mounted on the back of the machine. It won't treadle - the base is in the way.