Chuck Francis' ThinFilm decals are a wealth of information for those who want to know about lettering and were extremely accurate. The guides that came with the sheets not only gave information on the location and placement of the lettering but also gave the sizes of the various numbers and letters that were used.
As you noted, John, the O scale lettering was accurate and crisp enough to be projected back to original size. Truly a marvelous and historical body of work in and of itself. I know that his mission was the accurate modeling of narrow gauge equipment but his work also preserved the lettering and the schemes for posterity.