Yes, it is a 1985 model. It was part of the whole new line of small Merc's which were to be released for the 1986 season - a couple got out early.
Even if it is "dressed" as a Mariner, it is a Merc save the paint/decals. There was a line of Mariners built by Yamaha for Merc, this is not one of them.
The "newly designed" 20 replaced the 18 horse XD which was the sister motor to the 25 XD. In fact, if you took the hood off and hid it you would be really hard pressed to guess whether it was the 18 or the new 20 or the 25 for that matter - about 95% the parts were used on the new model.
Likewise the 25 XD was replaced with just the plain old 25 which shared everything with the 20 save the carb.
The model changed very little over it's lifetime which spanned until 2005 when Merc scrapped most of their 2 stroke line.
A great little motor, not as prolific as the 25 which was sold on thousands of "package deals", but since they share the majority of their parts, there is lots out there. With the electric start it is a desirable motor.
The latch you would be looking for is available through any Merc dealer. Most of the parts in the assembly sell for under 5 bucks a piece - unless you are partial to the bungee.
It would be well suited to a 14 or 15' aluminum utility with 2 or 3 passengers.
