What are '596 castings?

I was checking out a set of those 596 heads also and did a casting search on autohobbydigest and they indicated these heads were for a 318 engine with a (cast-in 360) indicated. Do they have 318 or 360 sized ports? Mike


4027596 1981-1983 318 HP (cast-in 360) 1.88" 1.60" 66cc - 72.5cc