After some back and forth, Bob agreed to letter the Mongrel Mogul for Texas shortline Moscow, Camden, and St. Augustine. As it turns out, this seven-mile railroad, which ran steam into the 1960s and offered passenger service into the 1970s, had only one Mogul, #201. Here is a photo of it in 1937:

Bob offered to decal the model with a lettering set, but I wanted to reproduce the font used by the prototype as closely as I could. The first step was to isolate the letterboard on the tender:

Next four steps are shown from top to bottom below. First, bring the photo into a drawing tool. I use Powerpoint, only because I have a lot of experience with it from the days when it was the only drawing tool that my employer would let me have on my computer. Second, because the photo is at angle to the side of the tender, stretch the photo out a bit to get back the approximately correct proportion. Third, insert a textbox, type out MC&SA, size it up to match the photo, and go through every font set on Powerpoint to find the one that is the closest match. The font set Square721_BT is pretty darn close once you toggle "bold" on. Fourth, modify the ampersand to better match the prototype. I used a combination of raster and vector drawing tools to do this. This was a tedious task, one not recommended for the impatient. I imagine that experienced graphic artists know a better way, but for one character, my inelegant method was sufficient.

The number on the cab was created the same way. The next task was to draw up the boxes that frame the lettering and cab number. For that, I had Bob measure the side of the cab and tender. I drew boxes the same size (shown in gray below), created the white letter box to fit, and sized the lettering proportionately. Non-intuitively, black graphics are required for anything that gets printed white. Finally, I then broke up the boxes into four separate sections, as I figured it would be easier to apply five smaller decals (four sides of the box and the lettering) than one large decal. These steps are shown below:

If Bob tells me otherwise, I will put the boxes back together before printing. Actually, I wouldn't blame Bob a bit if he skipped the tedium of applying the letter boxes, or if he used a paint pen to draw them instead. I drew them up as I was already in the middle of it and it would give Bob this option if he wanted to use it. Also, drawing the boxes now completes the set in case somebody wants to use them down the road for something else.
These will get printed on the Alps. I have left out a lot of details here. Specifically, there is a lot of back and forth between creating the graphics in Powerpoint and preparing the printer-ready version, which is mostly done in a dedicated vector drawing program (I use Inkscape, which is widely supported freeware). The learning curve is a bit steep. I wisely have kept careful notes over the years, as I create and print decals infrequently, such that I would be starting over each time without the notes.
Jim