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Have you checked/changed the gearoil? Forward is the default gear when no power is applied to the neutral and reverse coils use a volt meter or a test light and check for power going down to the coils in neutral and reverse with the key on run.
http://www.maxrules.com/graphics/omc/wiring/1972_65_Eshift.jpg
There are two disconnects on the green and blue wires just pull the sleeve back and check for power. Be careful you dont short them to ground.