The Peter Witt trolley will go around 8" curves.  The Birney will do at least 6" curves. 

Note that I did say "two of the three trucks", so it is a three-trucker.

In may case there were cracked gears in two of the three trucks.  I ordered the complete set of replacement trucks with metal gears from Bachmann.  IIRC, they were about $33 each.  Your description of the issue mirrors what mine was doing. 

The unit in front is a snow sweeper.  Under that tarp curtain is a big brush equipped with reed bristles to clear the track.  We had a similar one at our local trolley museum until a devastating fire destroyed about half their collection.  In the photo, its hard to say what has happened.  Might be that the track is iced up under the snow and the sweeper can't move.  Since the cars all seem to be lit, icing of the trolley wire is probably not a factor. 

Agree that blind drivers are relatively common in the prototype, especially for locos intended for branch lines, narrow gauge, and other instances where sharp curves are common.  Even the Pennsylvania RR's big 2-10-0 decapods were originally built with the 3 center driver sets blind.  Many were later modified to only have the center driver blind.  But many models have been made where the prototype did not have blind drivers but the model does in order to negotiate our super-sharp curves.  It's a trade-off and that's OK.  I would note that in almost all cases the tires on those blind drivers were about an inch and a half wider than the flanged ones in order that the wheel wouldn't drop behind the railhead on a minimum radius curve.   

We have to make compromises and trade-offs in the hobby all the time.  Dealing with curves is perhaps one of the biggest trade-offs.  The prototype describes curves in degrees.  A ten degree curve is considered sharp for main line operations.  Most main line steam locos could negotiate a 20 degree curve at very low speed (such as a turning wye).  The conversion formula for degrees to radius is:  5,730 divided by the degrees of the curve.  Therefor a 20 degree curve has a radius of 286.5 feet.  In HO this equates to 39.5 inches radius.  Most of us don't have the space to build a layout using that as a minimum radius.  So, models are compromised in design to handle much tighter curves so we can build a practical layout.  I would note that a lot of the brass imports of larger steam locos had minimum radii of 24 to 30 inch radius.  There were compromises in mechanism design such as longer wheelbase lead trucks, blind drivers, open space above the trailing truck where any ash pan should be, etc.  You work at your own comfort level.  Oh, by the way, that 10 degree main line curve equates to a 79 inch radius curve.

Assuming your locos are US market Bachmann models they will be just fine on Code 75.  Models that meet the NMRA wheel standards will operate OK on any rail down to Code 55. 

Really great model work.  I only have two small quibbles - the sound locos need to have the chuffs synchronized to the driver rotation, and there should be crews in the cabs. 

As Jonathon noted, you need to give the wheels a good cleaning.  Kadee makes a brass brush type cleaner that powers the loco while the brushes scrub the wheels clean.  Also, the track also needs to be cleaned periodically.  A rag and some alcohol will clean the gunk.  This is especially important if you have brass (as opposed to nickle silver) rail since brass oxidizes fairly quickly. 

No pics show for me.

I would note that the Bachmann model has both engines pivot, which allows it to run well on tight curves.  The prototype, and most brass imports, have the rear engine rigid, which REALLY accentuates the front boiler overhang.  Note that the old Rivarossi articulated models also had pivots on both engines for the same reason. 

I'm making an educated guess here, but I agree it is probably a boiler fill valve, and the round plate is an inspection port to check the flues and tubes back at the rear tube sheet.  And yes, likely Russian practice from the original order. 

I'm pretty sure that little Heisler is a fireless loco.  No visible stack and the fat boiler.  Heisler made a number of fireless locos over the years.  I saw one in operation at a power plant in Alexandria, VA back in the early 1970's.

Pictures stopped showing here after the pic of the Freedom Train.

Technical correction - The ACL loco is a 2-4-2, sometimes referred to as a Columbia type.  Common type for small switchers and tank engines, very rare as a main line road engine.