These are Rectify Series drop-in speaker systems for both Walthers Proto and Mainline F-unit locomotives, as well as late-run sound-ready Life-Like branded Proto 2000 F-units.
Two version are available, depending on which factory speaker/weight is installed in your version.
The WLPR-F701-RC1 uses screws throgh the frame's floor, accessed just behind the fuel tank.
The WLPR-F702-RC1 uses screws through little "wings" inside the frame, just behind the PCB/decoder.
In either instance, the speakers use the factory mounting screws and no modifications are needed to replace the factory speaker/weight.
The speakers come fully assembled and tested.
WLPR-F701: 31mmH x 18mmW x 53mmL
WLPR-F702: 23mmH x 27mmW x 49mmL