It looks great to me!
One thing I'd point out, though, is that you can't simply "greyscale" a RGB image and compare the shades of grey. Real B&W film (especially old vintage WW2 film!!) had so many variations in shades of grey for the same colors. Lighting, weather conditions, paint reflectivity, fading images after 60 years of archiving, bad chemicals in the original film, the developing of the original negatives, or even the development of the original prints, can all change how a "grey" looks on the final product. [EDIT: Not to mention the contrast, brightness of the original film! Was it high contrast? Normal? Low contrast film? It all affects how the pixels show up]
I'd go with your gut, go with other examples you know of, and use the best educated guess you can for colors. I wouldn't go on what it looks like when you set color mode to "greyscale"
Looks good, though. Almost like that 109F with similar dark wingtop splotches!