My guesses (I have not seen factory documentation for Chevrolet truck colors for some of these parts):
transmission - raw cast (changing to rust color, eventually)
clutch housing -
raw cast (changing to rust color, eventually) - engine color
"Cast Blast" is sometimes used to keep the "new look" on those parts.
GMC painted those parts non-gloss black
Here are 1950 Chevrolet truck color names - scroll down the three pages Here are color names and paint codes. Hopefully, someone will past information/links for modern equivalent colors for the interior colors.
