try to make this short. This is my first boat and I have a 1969/70 80 hp merc i/o with a prealpha lower unit, not sure what one though. it wont shift into reverse. At first it wouldn't shift into forward. with the lower unit detached from the boat we are able shift it freely between forward and reverse, no problems. put it back together and it will only do one or the other, strange sounding i know. it has a cable on the control unit which activates hyrdralics on the shifting dog. we have filled the resivoir and bled it and with the lower unit off it acts the way it should but together it doesn't shift both ways. I have three questions, 1) where do I find the numbers on the lower unit to determine exactly which one I have? 2) does having the engine running assist in the shifting? 3) do they make a conversion to make it all cable? any input would be great, my boat guy (he is the only one willing to work on my old girl) and I are at a lost. Thanks rounsy22