If it were me,
and I have the old belts which did fit and worked, I would measure them, like this....
https://www.youtube.com/watch?v=DYEk5UFyN94
to get their size.....
and I would got to this chart....
http://cubfaq.com/belts.html
to find the belt sizes(s) in red, that you measured, and you will have your part number. Voila!