While the OAL of the valves is equal the margin on the exhaust has a little more area between the margin and the face. You should see this when checking valve spring installed height as well. I'm 99% sure that is why you are seeing a variation from intake to exhaust.
It's the geometry effect of the offset intake rockers. Picture a triangle that starts at the lifter: the vertical line represents the pushrod length for the no-offset exhaust rocker; the horizontal line at the top of the triangle represents the intake rocker offset; the angled line from the lifter to the other end of the horizontal line is the longer pushrod for the offset intake rocker.
Exhaust valve lengths for inline valve engines are usually longer than intakes because of the thicker valve margins. The effective seat-to-tip lengths are virtually the same.
