If its a GM roller cam, use a melonized iron gear.
from GM:
"Note 2: Distributor P/N 1104067 or melonized distributor gear P/N 10456413 must be used on all crate engines with steel camshafts."
If its a billet roller cam, use the bronze or composite gear.
Some roller cams can be ordered with a cast iron gear, and use a regular dizzy gear for a flat tappet cam (Howards cams can be ordered that way)
I've seen a GM roller and a cast iron gear together, It sharpened the teeth within a few hundred miles.
Find out what / who's cam it is.
Dan'l