[JasonB]

I can't find a font that matches, but as Tamar said it's likely hand painted. It certainly doesn't match the traditional Cummins typeface which is apparently Helvetica Neue 85 Heavy.

Nice work from Leo, that slightly larger "S" in diesel is very distinctive.

Looking at photos of the car though, it seems they used a backwards slanting typeface as well as the traditional italic, at different times.