[Rich Biebel]

The X was found on a number of different castings including '441's

The '461 X was the most popular head in C/SM when that class was so popular. It did have larger intake runners and since porting wasn't allowed that's the head everyone tired to get.

I've seen other casting numbers with an X in various places but it usually didn't mean anything as far as runner size when we checked them many years ago

I've seen the X on the casting surface in various places and down inside the water jacket with the head facing you chamber side up....

Maybe there are people that know for sure why that was there and if they are any better but I am not one of those folks...