B&O diesel lettering for most early diesels (1943 - 1962) was a custom B&O font, an extended Roman.    Five inches high.

Color was Dupont Imitation Gold, a dark spicy mustard color.  Not gold leaf.  Not Big Bird yellow.   Not the later Federal Signal Yellow.

Look at B&O passenger letterboard decals in a satisfactory imitation gold.    The spacing will be different on diesels, yet you will get extended Roman fonts, five inches high.