These are two different Rectify Series drop-in speaker systems that fit most (if not all) Walthers Proto locomotives with a 28mm speaker sandwhiched between frame halves. The speaker mounts in the factory cavity and no modifications are needed to replace the factory speaker. Either system should fit any of the Walthers Proto models that use this type of speaker mount.
WLPR-UNI1-087 features a larger enclosure and does away with the speaker-frame half. A dab of adhesive holds it in place and the speaker fires down over the truck. This speaker has a fuller sound than the UNI2 model.
WLPR-UNI2-087 seats within both frame-halves and fires to the side. Its smaller enclosure permits replacing the speaker-frame half back in place. Bits of tape should be placed over the speaker contacts to ensure no shorts occur. It does not sound quite as full as the UNI1 model, but is for modelers who want to keep the frame-half in place.
The speaker comes fully assembled and tested.