Re: Help Trying To Identify What Model An Year Mercury 40 Hp
Motor is definitely a 1979 Mercury 40hp 402 as was indicated earlier by skimmer.
It -might- have a charging system. Look for yellow wires coming down from under your flywheel, and see if they go to a rectifier (small square item with 3 terminals, as per image below) and then onward to the red lead on the starter solenoid. If they do, you are charging your battery.
The 2 cylinder Merc weren't known to be the most reliable motors they ever built. Street value is too dfficult to judge sight unseen.