I used to own the Dragon many years ago. If what you mean by the "center absolute point" is adjustment of the heads for identical record/playback parameters going in both directions, I think you need a 'scope to adjust them. If I recall, the manual said nothing about user adjustment.
There are screws near the heads for those adjustments, but I think they're really for the technician's use. When I owned the unit, I did play around with the screws (to my chagrin) and had to readjust them by ear.