Evinrude 55 not shifting.

[Wishniwasfishin]

Just purchased a old 78 invader with a evinrude 55 horsepower. Motor runs great. Won't shift into gears. Pulled plugs shifted into gear and can't turn prop. Prop spins in neutral. Drained lower unit a very small amount of metal shavings came out. Nothing bigger than a spec. Pulled prop everything looked fine. Im assuming something needs rebuilt. This is my first boat. I am trying to find a Manuel on the motor now. Any help would be greatly appreciated. I do not know the year of motor. The model # 55975c