Towards the end of the Storm Series production lifetime (1968-1972), Ovation implemented several changes to the line.  The most obvious was the change in the neck attachment point.  These later models, so called "long necks", had the neck attachment moved about 1.5 inches away from the pickups.  The bridge was also moved, so the scale length actually stayed the same.  The second change was to introduce model numbers.  Shown below is a blonde finish Thunderhead, model K-1233-4 manufactured in 1972.  The Thunderhead came standard with gold finish hardware and pickups, but the example shown below has had all the hardware swapped out for new chrome, including the second generation chrome pickups.