How 'bout a new thread, unexplainable Railroad equipment! Found this little kitbashed loco searching Google.... All I could find as far as history, it's a AP1620A, and from 1974.
Reminds me of the Johnny Cash song "one piece at a time". I did find a Ferrocaril del Pacifico roster which indicates that it was rebuilt from an RS11. https://www.thedieselshop.us/FCP.HTML
It looks like a modeler's Saturday afternoon kitbash project from whatever was on hand in the scrap box. I give the Ferrocaril del Pacifico shop forces high marks for their resourcefulness.
The "Second Diesel Spotter's Guide" describes 4 such units were build by N de M in it's San Louis Potosi shops, all looking different. I found pictures of two of them: http://www.rrpicturearchives.net/showPicture.aspx?id=844291 http://www.rrpicturearchives.net/showPicture.aspx?id=1875568
Those Mexican kitbashes are crazy things - once again proving that if you can imagine it, there's prototype for it. So you take one RS-11 frame (maybe even a homebuilt frame, from the looks of it), trucks and engine hood, add an F-unit cab, and to spice it up, a home-made windshield and nose. Clap the whole thing together and voila! One wacky locomotive. Serves four. I remember an article from the mid '70s on one of the model railroading magazine showcasing some of those Frankenstein creations. There were some weird ones, and a lot of Mexican kitbashes. I don't remember which magazine it was (I was in my early teens). So if you believe that SWeeps and Beeps are odd, look south of the border, down Mexico way...
