Hi,
with that arrangement I would use an inline gear box with the pulley on the output shaft.

https://www.ebay.com/itm/25467196994...Bk9SR9DD-oDYYQ

You can select the gear reduction from as little as 5:1 up to 100:1 and it accepts 60mm steppers or servos. Just chose the gear ratio to get your desired torque.

Craig