Small block water pump pulley question

There is a cast Water Pump and an aluminum one. I think the cast is 69,and they went aluminum in 70. there are different pulleys I think between the two as in a 69 pulley may not work on a 70 aluminum WP and vice versa. I ran into this on my 70, I had put a cast iron WP on, pulleys wouldn't line up,so I had to pull the cast iron WP and install an aluminum one.