This is the best way to reproduce prototype lettering, logos, etc. This is the method I, and likely most other artwork people, use in order to get proper fonts, etc.
Even though there a railroad fonts around, the railroads would often change. In particular the "good olde days" the lettering would vary from order to order or even from shop to shop. There wasn't any big, huge printing presses printing big huge vinyl decals. It was all done by sign painters at each location, and different sign painters even at the same locations. While there may have been stencil for the smaller stuff the bigger lettering and logos were often made by laying out the design on paper and then punching many small holes by using a pounce wheel (them things used by modelers to make rows of rivets in a hurry). Then the paper would be taped to the car side and powder puffs were used to put the design on the car with powder. Remove teh paper and teh sign painter would use the powered dots as a guide for the actual paint. Lots of room for variations here. Plus, each run of cars would have new artwork drawn as the chances of one layout being identical to the next project were practically nil.
THE best way for getting the correct lettering is through prototype photos. They CAN be manipulated to remove any perspective and resized if any dimension is known. That can be size of any lettering, any dimensions of the car itself and, if all else fails, the rail cars wheels. I often use that; I draw a scale 33" square that is placed over the the most visible wheel (this is all on computer of course) and then get it to fit in the box. From there it is a rather simple matter to square up the side and/or ends of the car.
Do this using Illustrator, CorelDRAW or another vector drawing program and the results can be scaled to what ever scale you want from 1 to 1 all the way to Z.
Oh yes. the idea of finding a commercial font that will match any lettering is not going to happen. Maybe on the small lettering a commercial font will be close and can, with manipulation be pretty close but even then certain letters will have to be redrawn. Even if you find a font for your railroad it will likely be entirely accurate for a limited number of applications. I have downloaded three versions of Railroad Roman and they are all different and generally speaking, eahc will have to br reworked to some extent to match the "Railroad Roman" in whatever photo I am using for a pattern.
The only skills this requires is familiarity with the program being used and lots of patience.