"Is it worth it? Should I even touch it with the serial number gone?"
I would not worry about the serial number. The step up Sherman auxiliary trans and the grader blade add to the value. Subtract them and you get to 1200 to 14oo which is not a bad price for a running 2N with OK tires. The smoke out the breather indicates blow by or else in cold conditions indicates condensation in the crankcase. Does the problem lesson when the engine warms up?