Yes. Flat River was on the very western end of the Illinois side of the Missouri-Illinois.

I have Charlie Duckworth's M-I book and have molecularly read it cover to cover.  It definitely is my kind of Railroad.

My friend used to see M.I. Box cars with the Missouri Pacific Buzzsaw herald in the yard back home in the early 60s. He thought that they had forgotten to finish painting the "P" on those cars.😂😂

There are several great photographs around the M – I in Flat River in the 20s. There was also an electric interurban railway in that area that is covered in his book some. One of the photos has a Pacific going around a curve in front of the depot, with overhead catenary wire for the electric operation above the track.

Scroll down to the 2-8-0's.  Look at the 1019 and the 1025.  These little ex-Frisco engines are right up your alley, and they are some of the very ones that ran on the branchline back home that I saw as a child.  The three swing bridges on the branch could take nothing larger.

http://www.trainweb.org/screamingeagle/loco_steam.html

You can add Pacifics to your short line steam locomotive list.

U S Sugar at one time ran four ex-FEC Pacifics, 3 of them survive today.

https://www.ussugar.com/u-s-sugar-steam-locomotive-no-148-hauls-sugarcane-train-to-mill-ending-harvest-season-new-sugar-express-launched/

And, this article is out of date, they're in the process of restoring the engine to operation.

https://www.trains.com/trn/news-reviews/news-wire/u-s-sugar-interested-in-acquiring-second-steam-locomotive/

After learning about all of this, I immediately put my USRA Pacific at work on the locals.

The New York Central ran Pacifics on some local and branchline freights quite a bit too.

You should read up on the Missouri-Illinois. I believe you would like it. A 110 mile short line that ran on both sides of the Mississippi river with a car ferry connecting them. In relatively modern times it was run by the Missouri Pacific, and the engines were lettered just like MP engines, except instead of Missouri Pacific up in the coal board, the tender said Missouri-Illinois. Plus they ran MP equipment a lot of times. They ran doodlebugs too.

http://laiben.com/wordpress1/about/

You really need to include the decapod in your list of short line engines. That engine was smaller than many consolidations with an extra set of drivers to spread the weight down over poor branch line and short line track. 
I have every modern 4–4–0 and 4–6–0 that Bachmann ever offered. but I run nearly all my locals with my decapods. 

Plus. About that Bachmann consolidation. While it is definitely a large engine, it is astonishingly close in profile and detail to a Missouri pacific spot – class 2-8–0, numbers 1–173 and general Missouri Pacific practice.  I think they are perfectly acceptable to run down a branch line.  Both those engine styles run regularly down my branch. In fact, my trains have gotten longer, almost to 10 cars a lot of the time, very long heavy drags on my little Railroad.

I remember in high school going nutsy-cuckoo over a NWSL logging mic for sale at an NMRA regional meat. Of course, I couldn't afford it, but I never forgot about it. Those things ran all over East Texas on various logging roads not too terribly far from my boyhood home. And I always wanted one. I doubt if anyone ever brings one out in plastic, they are just too specialized and and small of an engine when everybody wants Big Boys and northerns because they've seen them on excursion trains. I already had the Wabash mogul and the ma & pa 10 wheeler, the same locomotive is Bachmann's present low boiler 10 wheeler.

I myself would like to see a plastic version of Varney's Old Lady consolidation, a beautifully proportioned small engine that I always liked, but never had.

When I was a kid, I didn't know all about the big, bad world and all of its problems. I only knew that the sun was shining in my world, it was a beautiful day, and the only responsibility I had was to play.

Sometimes with me, it's sort of like that with this decoder business. I still remember the first DCC/sound locomotive I bought, a Soundtraxx sound on board Bachmann 2-8-0 way back in 2007. Plus one of the first run decapods with the same decoder. I bought an EZ because I was intimidated by DCC and was told that the EZ command was the easiest way to get started it, for $75 or so with the time. I didn't know how to change any CVs and was happy just running the engines back-and-forth on a simple run around track deal I had on a 1x8 board, blowing the whistle and ringing the bell. It took me over a year to get the confidence to become involved with a more advanced system. But I have to say, I probably had more fun than today with those two engines just the way they came from the factory.

It only solves sound quality issues at higher volumes. It doesn't allow adjusting of all the other individual CVs, for the various sounds.  To do that you need some device capable of actually changing the cv volumes to suit.

I myself like using the programming on the main option in a DCC system like NCE wireless pro cab that I've been using for about 15 years now. You can actually raise the whistle up and down while the engine is running, to see how well it realistically covers up all the other sounds.  Some of the old soundtraxx sound-on-board products that were factory installed in. Bachmann engines had very anemic whistles. According to my friend who works out there, Tsunami2-2 has a much better amplifier and you can't turn the whistles up all the way without distortion. After programming a few engines with tsunami 2–2, you start learning the limitations.

Lets you keep the basic EZ command. But. After getting a more advanced wireless DCC system, there is no going back to the EZ command. I gave it to a kid who was just getting started in model railroading.

Still ..... QSI is gone, and any decoder made today will far surpass any of those early sound units.

😂😂😂

And QSI is no longer in business.  Today's decoders are astronomically better anyway. My personal preference is Soundtraxx, at the moment, Bachmann appears to prefer TCS decoders.

One thing that I do not like about the Alco 2-6-0 is the tender. With those goofy excessively high coal boards, it is too idiosyncratic to look like any  other Railroad beyond the odd little short line engine that Bachmann decided to replicate instead of a more common type.  Bachmann used to sell separate tenders, including the one presently behind the low-boiler 10 wheeler.  That particular tender would really help that mogul resemble other engines.

The other thing is the puny headlight. The N scale model looks infinitely better with a larger headlight on it. But, on this model, Bachmann finally got the headlight bright enough to be a headlight, in comparison to the terribly dim headlights in their  earlier spectrum engines, especially the consolidation.

I too would be thrilled with an eight driver frame under the present Alco  2-6–0. It would begin to bear a great resemblance to the Mississippian #77 that I saw running up in Mississippi in 1964, or even more meaningfully to me, one of the little Missouri Pacific ex-Frisco 1001 class 2–8–0's that I saw running in my hometown in the MP last year of steam. I've actually quite often thought of such a job, but you are much braver than I.

My old layout tries to capture the aura of the old Missouri Pacific branch back home now long gone, passing through low, lying, wetland, woods and agricultural country.

That must be very old technology. It sounds like a very complex way to change CVs. I've always programmed on the main with my N C E procab or on a programming track with the pro cab if I needed to do a bunch at once.

Didn't we talk about this before in the old forum?  I agree totally and also have ideas about suitable prototypes.

Short line modeling is a concept that usually takes some tenure in model railroading to understand.  It's so much better and realistic in limited space than trying to squeeze a Big Boy into a phone booth.   I was lucky,  grew up in a time and place that had two branchlines that ran this very type small steam engine, I saw them in every day service.  So I tried early on as a model railroader to recreate these places, and I am still at it. After almost 60 years, I'm still building the same Model Railroad.  These vintage style branch and short lines basically don't exist anymore in their old form, and live on in the memory of people like me.