Often, a "reject" from one "line" would be restamped more "accurately" (like a 12 with too much chamber volume COULD become"13"). It' unusual, but not unheard of.
13s are not "Ram Air" heads. NO "d-port" head is, as ALL of them were used in non-Ram Air applications. Please reserve the name "Ram Air head" for small-chambered "round port" heads.
These heads will require a rather large "dish" in the piston for using 93 octane gas. Static compression is WAY too high with flat-tops.
