Way back in the early days, and continuing to some extent today, manufacturers had to make some choices - model a particular road's locomotive, which might well limit its market and reduce sales; make models of locos for big, popular railroads that would draw in fans of those roads; make a "generic" model that resembles several prototypes and let the buyer do as they might with paint and decals.  Examples - Mantua made kits for several Reading locos in the late '40's/early '50's.  They were brass and cast metal.  When Mantua decided to go more mass market, they opted for the more generic all cast metal models that kinda/sorta looked like something on your favorite road.  Varney pretty much followed the same pattern.  Back then, a lot of modelers were just happy to have something they could build and run.  That's why you saw a lot of Docksides and NYC Hudsons in layout photos of the period.  This eventually opened up the market for imported brass models, which mostly modeled a very specific loco or class of locos.  You could get a nice Pennsy K-4 kit from Bowser, but if you wanted an earlier K-2, then a brass model was what you bought.  The Bachmann Connie is probably closest to an Illinois Central loco, but it is close to other roads' power and if you're into some superdetailing you might get pretty close.  See Jonathon's reworking into a very credible looking B&O E-27. 

Another aside - ET&WNC Ten-Wheeler No. 8 came second-hand from the Twin Mountain and Potomac RR.  The "Two Mules and a Pony" was an very obscure little 3' road that ran from a connection with the B&O at Keyser, WV to Burlington, WV.  The road only lasted from 1913 to 1919.  No. 2 went to Tweetsie.  No. 1 seems to have vanished.  Speculation is that it went to a logging road. 

The Interstate RR, way down in southwest Virginia, also used the orange and cream colors on its diesels.

OK, clue me in.  Did Bachmann release a new run of the Russians?

As a general rule, most all the nuts and screws on Bachmann models are metric.  For best fit, you need metric hex drivers.  I believe Micor-Mark sells a set. 

Some compromises have to be made to get a model locomotive to run on a typical model railroad.  All the previous info offered is good.  But prototype locos are generally not intended to negotiate the type of curves we use.  A very sharp prototype curve comes out to about a 30" radius in HO.  Most of our diesel models will operate down to an 18" radius, which means some compromises in truck swing, coupler length, piping locations, etc.  Steam models have it worse because of the space needed for pilot and trailing truck swing.  The long rigid wheelbase of the drivers limit curve capability unless some lateral play is designed in and/or some of the drivers have no flanges.  The spacing between the loco and the tender may have to be wider than prototype as well. 

In general, whistles were the choice of the buyer.  In most cases with small locos like the Porter, they just ordered a "tweeter", a high single note sound, rather than a big chime whistle you would find on a big road loco.

The PRR K-4 Pacific has 80" drivers, which should be "close enough" to what you need. 

AFAIK the Bachmann wheelsets comply with the NMRA HO standards.  I've never had any issues with them.  Never hurts to check any wheelsets with an NMRA gauge for tire width and flange depth.  I would note that HO, On30 and On3 all use the same wheel and flange standards.  The only difference is that On3 is a wider gauge than HO/On30.

FWIW, I try to match the 4 chuffs per revolution at fairly low speeds.  Once you get up to "road speed" you can't really see whether the rate is exactly 4 per rev, whereas at low speeds you can see if the chuffs and revs are in sync.

What is the radius of your curves?  If they are 18" (or less) it is likely that the loco is binding a bit on the curves due to its long wheelbase.

I'm at least hoping they will keep the Stanton trucks in catalog.  I have a couple of old trolleys that need major power upgrades.

I see no one has responded as yet, so here's a suggestion.  I couldn't find a photo of the model good enough to see the tender trucks.  If you can post a pic of the undamaged truck here we can then see what might work.  In general, six-wheel tender trucks were either Commonwealth or Buckeye.  Brass versions of both have been made and can likely be found on e-bay or at a good train-oriented hobby shop.  The other option is to get to one of the big train shows and see if you can located a spare tender or the truck itself.

I'm pretty sure that what is in the pic is a cylinder and valve casting, not two cylinders.  Casting technology had not yet gotten to where and entire cylinder block could be cast as one piece.  So this is one half of a cylinder/valve set.  By the 1930's/early '40's casting technology had advanced to the point where entire engine beds - frames and cylinders, could be cast as one piece.  \

There were a few cross-compound locos built around the turn of the 20th century.  They had a high-pressure cylinder on one side and a low pressure cylinder on the other.  There was also the Vauclain compound, designed by Sam Vauclain of Baldwin.  There, the high pressure, low pressure and valve were all cast together, which gave a distinctive appearance to the cylinder assembly.   

Just a bit of history on the Ma and Pa switchers, Nos. 29 and 30.  No. 29 was built in March, 1913 with a wood cab and Stevenson valve gear.  No. 30 was built 8 months later, but came with a steel cab and Walschearts gear.  Westside brought in brass models of both locos back in the early 1980's, IIRC.