I see there is still a lot of the black goo from the old rubber in the pulley. That needs to be cleaned with naphtha or lighter fluid will do nicely, otherwise the new belt will stick to it.
That plastic ring- cut it off. It breaks off that smoothing roller. Or take it apart like I used to do. I used to take the arm off, add a layer of tape to the plastic where the brass roller fits to take up the loose play. Sometimes the bottom would break off instead, allowing the brass part to fall down actually drag on the tape since it couldn't turn.
Those were not particularly reliable machines even back in the day.