These are Rectify Series drop-in speaker systems for Atlas Master MP-36 locomotives. The speakers use a strap of tape to mount and no modifications are needed to replace the factory speaker. Just be sure to keep the AHGS-SPDS contacts from pressing against the chassis.
 
The AHGS-SDPS-RC1 is a front-mount speaker replacing the stock speaker. If choosing only one speaker, this would be my preference.
 
The UFIT-30D9-RC1 is a rear-mount speaker option. This speaker can be wired paralell (LokSound) or series (Soundtraxx, WOW) with the AHGS-SDPS front-mount speaker. DO NOT use this speaker with the stock speaker wired in parallel; if keeping the stock speaker, you MUST wire the two in series regardless of the brand of decoder you use.
 
If you need a 2pin wire harness, the "Medium" harness will fit: https://www.scalesoundsystems.com/product-page/factory-pcb-speaker-harness-medium
 
The speakers come fully assembled and tested.
 
VIDEO: https://youtu.be/StMmU1g1qhI