Mounting Encoders to Motors/Gearboxes

My team received encoder kits (https://firstchoicebyandymark.com/fc-cu-4681) from first choice and would like to use them on our shooter and possibly intake. We understand how to mount them to the motors, but how would the gearbox fit on afterward?

It seems that attatching the encoder to the motor means that you can’t attach the motor to a gearbox. If you want to use these encoders, you’re probably going to need to make a custom gearbox with a place for the encoder that isn’t on the motor.

I’ve never used these, but that’s my best guess.