1960 Kiekhaefer 150 Mercury 15HP - Shifting Question

[dsp3930]

Where would be the best place to start with this engine to determine issues with shifting out of Foward.

It will not shift into Neutral/Reverse.

 

[Chinewalker]

Getting an OEM service manual. That's an automatic transmission motor and there really isn't any easy way to explain the ins and outs of setting them up here...