Yes, it is a 1968 model.
Seloc's produces a manual to cover your model (1965-89, 3&4 cylinder models). Provides everything you need to do upto/including a total rebuild.
Is it worth fixing? That's a personal question that only you can answer.
If the ignition is totally functional then the motor is viable - if not then you are really out of luck. The distributor (and related parts) and the stator is so long discontinued that even getting parts from a recycle place is somewhat of a challenge and very expensive if you can find them.
Carb kits and waterpump parts are still available from Merc as are other little odds/ends that you may need.
Now, if you have a 1960's Mahogany Lapstrake runabout and want a period motor to hang on the back for that "authentic look" then this could be your motor.
If you are looking for a project to kill some time with, this could produce a "cool motor".
If you are looking for an everyday motor to try and get running well enough to use on the weekend for fishing or tooling around, I would personally be inclined to invest my time and money into something else.
