Hallo Kristof,
several customers are using this parts in combination. But you should check the belt position. If it is going too high, use a wider washer ring between the pulley discs. Serial is 1mm, people say there is a washer with 1,3mm available from Piaggio. Use SR2017/6- , not SR2117/6-
They weight should be same like the Malossi rollers or a little less.