Your first task will be to remove the old Cheapskate carriage from the tower you'll be installing this new carriage on. I recommend working with one tower at a time. There's no need to remove all three carriages at once.

Install two RZ44 rollers and a spring arm on to an inner carriage half. Make sure you match the spring arm orientation as shown - installing it backwards can damage the spring arms!

Route the two belt ends through the face of the inner carriage and attach a binder clip to the ends. This will prevent them from slipping out of the carriage while you're working on it.

Clip the carriage on to the tower by setting the left pair of rollers into the tower groove and then the right. The spring arm should provide plenty of tension to hold the carriage in place.