These are Rectify Series drop-in speaker systems for Athearn RTR U50 (not Genesis) locomotives. The rear-mount speaker uses carpet-tape or a touch of adhesive to secure it to the frame. The front-mount speaker uses the factory mounting screws. No modifications are needed.
 
The speaker comes fully assembled and tested.
 
Dimensions are:
26mmH x 18mmW x 24mmL (rear)
10mmH x 18mmW x 29mmL (front)
 
VIDEO: https://youtu.be/f6jvmz6r66Y