!980"s lower unit problem New Help appreciated

[ernesttodd1]

I just bought a 1970 silverline 16.5, w/evinrude 70hp outboard. I am a mechanic but am not too experianced with outboards. anyway the lower unit will not turn but you can put the motor in gear but the prop barly moves. but yet when you shut her down,you cant turn the prop?
what can i be expecting to get into? any help is greatly appreciated and i am good with engines, mayby i can answer a few.
thanks Todd