This is a picture of a 1967 L35 cast iron pulley P/N 3873847. I looked closely and it appears semigloss. The pump is gloss black.
I know you asked for 1968, but so many 67 parts and finishes were carried over to 68 so perhaps this is the same for yours?
Do you have the cast iron crank pulley too? I examined that and it looks to have a gray phosphate finish. I can provide pics of that if interested.
Again, this is for a 67 L35 MZ w/K19 smog pump.