I remember when I built my first engine in 1973, a '53 235 powerglide, I was surprised that the new pistons were aluminum. All the old books and manuals I had read indicated that the Chevy had CI pistons. I had taken a few old lawnmowers and compressors apart as a kid, and they had CI pistons.
I have also rebuilt the motors in various tractors, all had cast iron pistons, and the tech literature referred to the pistons as CI. I chose to use NOS CI pistons in a couple of them because newer piston were high compression aluminum, and would prevent me from running the engines on keroscene.
So you know what? It sure would be easy, depending upon what you have read and worked on, to assume that CI Is the normal and usual material for a piston, until you find out differently.
I think the guy was doing the right thing by asking the question, because then he would get a little assurance that he was on the right track, and find out what his options were.
Just my 2 cents.
Kurt
