All the spread port intake will interchange, 18 14 11 etc. The intake manifold faces are all the same angles, the degrees are referring to the valve angle from deck surface.
OLD 18 degree castings (1990's) were not spread port like the heads available now.When I worked there ONLY the 18* intake would work with the 18* heads. ONLY 14* and 11* heads shared an intake. 18* head castings were there own and 14* and 11* heads shared the same casting.