This is a Rectify Series drop-in speaker system for Atlas Classic (Kato) RS-1 locomotives. The speaker uses a touch of adhesive or double-sided carpet tape to mount to the frame posts and includes a hole for routing the truck and speaker wires through, keeping them clear of the drive-shaft/flywheel. You will need to remove and trim the stock light-pipes, leaving only the last 1/4" or so for the lens with 1206 LEDs glued on.
You can choose to install only one of these in the long hood. This would leave room in the short hood for a stay-alive if desired. An ESU Loksound Direct or Soundtraxx Tsunami2 PNP will fit perfectly.
If you opt to install two speakers and still want a stay-alive, use of a TCS AK-MB1 motherboard can be deployed. A Loksound 21-pin decoder will just barely fit; a TCS WOW-121 decoder will fit comfortably; a Tsunami2 21PNEM will not fit due to it's increased height. If you want two speakers and a stay-alive, you may be able to use a Loksound Direct or Tsunami2 PNP and nestle a TCS KA1 KeepAlive® on top, but I've not confirmed this.
You can find a simple installation guide here: https://www.scalesoundsystems.com/guides
The speaker comes fully assembled and tested.
Dimensions are: 10mmH x 17mmW x 30mmL