Ok, lots of confusion here
Fist of all, it sounds like its a Johnrude Oceanrunner series with opical igniton. Pretty good motor, lighter than most. Its whats referred to as an Eagle Series. Its not as big or heavy as the 200/225 loopers. Bad part is parts are starting to dry up for them as Bombardier is starting to reduce inventory of older motor parts. Yamaha made s Saltwater Series and used carbs or the OX type fuel injection. I don't think this motor matches the details you've given. If the motor mentioned is a nice clean fresh water motor, then its worth that much at a premium.
As far as you going back merc, I've got a 5" extension and several 25" lower units laying around. Once I get this one boat
in my yard finished, I may be able to free up some parts if you need.