Hi, welcome to the hobby. I have lots of information to share with you so I hope this isn't too much.
But before I go into too much information, I have some bad news if you want to stay prototypical. K-36 locomotives did not run on the Silverton Branch all the way to Silverton until the 1980s. Yep the 1980s, after the D&RGW sold the line.
The Silverton Branch could not handle anything larger then a K-28. The D&RGW planned to improve the line to handle K-36 and potentially K-37 locomotives, but this never happened under their ownership. It wasn't until Charles Bradshaw purchased the line and created the Durango & Silveton Narrow Gauge Railroad in 1981 that improvements to rail, cuts, and bridges were made to handle the larger locomotives.
About the farthest up the Silverton Branch a K-36 or K-37 could go was Hermosa. And even this was iffy due to the weight of the locos on the track through the marshland north of Durango...the area near the hang glider park and Dalton Ranch in present day. A K-37 did makes it way up north in the 1960s on a ballast train, but it did not go any further then Hermosa or possibly Rockwood...I can't remember exactly how far it got but not too far up the line.
Sorry for this news as you like the K-36. However there's nothing stopping you from running these larger locos, so if you like them run them
Aside from the K-36 info I posted above, I want to address some of your other questions.
First, the era (pre WW2) and appropriate lettering/paint
If you really want to model pre-WW2, then the railroad on the Silverton Branch would be the Denver & Rio Grande Western (D&RGW). The Durango & Silverton (D&S) was created in 1981.
A good modeling era to shoot for (based on available equipment in 1:20.3 scale) would be the 1930s. In this era, you will want to go with the Round Herald (sometimes refereed to as the Moffat logo or Royal Gorge logo depending on the wording in the logo).
So equipment with the logo seen below works for this era:
The "flying" Rio Grande logo was adopted in 1939. Because it took some time to paint everything, especially during the war years, the flying Rio Grande logo is best for during and after WW2 and not so much for a pre-WW2 layout. This logo looks like the photo below:
Also prior to WW2, all maintenance of way (MOW) equipment was painted red. The gray color was during and after WW2.
Second, appropriate locomotives
The most appropriate locomotives for the Silverton Branch in the 1930s would be a K-28, K-27 or the lone C-25 #375. Accucraft has a K-28 and K-27, Bachmann has a K-27. But I do not believe any model of the unique C-25 #375 is available yet. Smaller C class locos could also be used, such as a C-19, or C-18.
Of these, the K-27s seemed to be the workhorse locos on the Silverton branch during this time. Of note is the large pilot wedge plow they used during the winter. Rocks from snow slides in the deep canyons on the Silverton branch prohibited the use of rotary snow plows.
I don't model the 1930s, but I believe these large plows were used during this time.
Third, scale ... and D&RGW or D&S
The proper scale for American 3 foot narrow gauge running on G scale track is 1:20.3.
Accucraft and
Bachmann make excellent products in 1:20.3 scale. Lesser know Berlyn Locomotive Works also offers some nice locomotives in this scale.
If you go with 1:20.3 from the start, you be running the correct scale on G scale track.
But I have an important question, do you wish to model the D&RGW, or the present day Durango & Silverton? Accucraft does not offer much, if anything, lettered for the Durango & Silverton. But if you really want to model the Durango & Silverton, then you might want to consider 1:22.5 scale instead of 1:20.3. 1:22.5 scale is slightly smaller then 1:20.3 but still runs on G scale track.
I only mention this, because
KISS (a German manufacturing company) makes a K-36 lettered for the Durango & Silverton. These locos are very hard to find, but living in Denmark, they might be easier to find. I purchased one from
Big Train World which is located in the Netherlands, as it was very difficult to find one competitively priced in the United States.
Here is what their Durango & Silverton K-36 looks like:
And LGB/Marklin makes Durango & Silverton painted coaches that look very nice behind the KISS K-36.
So this might be an important decision depending on what railroad you really wish to model.
We model the D&RGW of the late 1940s to early 1950s in 1:22.5 scale. Take a look at our layout website for some photos:
Snowshoe & San Juan Model Railroad Website Link
Fourth, track
On our layout, we use code 250. Code 332 is more readily available, but the rail height is extreme for narrow gauge. So that's why I prefer code 250.
We use
Llagas Creek track, specifically nickel silver code 250 with "narrow gauge" ties.
Fifth, research
There have been loads of books published over the years on the D&RGW and the Silverton Branch. Two good ones that cover the Silverton Branch in depth include:
Cinders & Smoke
Durango, Always a Railroad Town
I hope this information has been somewhat useful.