This is definitely a MARINER, model year in the 1969 to early 1972 range. The deck design was changed to the one now used by Stuart some time during the 1972 model year run. This version was more or less an update of the original Mariner design from 1962-68. for 1969 the cabin was enclosed with an aft bulkhead and the cockpit became self-bailing. This change allowed 2 aditional berths inside the cabin under the cockpit seats, the forward berths that originally were 2 singles meeting near the bow, now was changed to a V-berth that slept 2 persons, hence...2 + 2 and the Mariner 2+2 was born. The cabin trunk shape design (stepped) was more or less carried over from the older 2-berth version keeping the forward hatch and adding a sliding hatch over the companionway (cabin entrance). When the deck was redesigned (to single level) sometime in 1972, the forward hatch was eliminated.
It is dificult to "nail down" the exact model year of most O'DAYs built prior to 01November 1972, since the older boats did not have the 12-digit HIN that includes the model year in the code. Boats built prior to the HIN requirement that started in November 1972 had 2 numbers to ID them, a Hull# that was based on total boat production of all O'DAYs, and a CLass# that refered to how many of that class had been built (in this case Mariners). O'DAY seems to have phased in the HIN on their boats and so it is worth looking on the outside of the transom near the starboard side for a 12-digit code that will start with "XDY" and end with (usually for this vintage) the last 2 numbers in the 12-digit code being the last 2 numbers of the model year ("72" for a 1972 model).
