"Rick, you are trying to turn
"Rick, you are trying to turn the driveshaft by hand (with the lower unit off the motor)? or you are trying to turn the prop shaft with the lower unit connected to the motor?
There is a couple of different shafts with regards to the lower unit, you will have to give a better description of what you are doing...
And just fyi your motor is either a 1992 or 1993 model, built for Sears and sold as a Gamefisher. The exact year can be determined by the Merc serial number which is most likely on a welsh plug on the water jacket of the motor."