I think what he is referring to is the 1.5 ratio and 1.6 ratio - Most heads will work out of the box with the 1.5 ratio - 1.6 usually requires some enlargement work on the push rod holes - (Long and short rockers is an old Chevy term)

The other rocker Sharp makes is the offset for the Indy style head or others like the victor head that requires an offset intake