Re: replace water pump on 1970 chrysler 9.9
If the lower unit is not moving at all, then the drive shaft is corroded into the crankshaft. Nothing you can do except force it. This will pull the drive pin through the water pump, breaking either the pump housing or the drive pin and ruining the seal.
After removing the lower unit, keep spraying the driveshaft with penetrant with the engine upside down so the penetrant runs down to the crankshaft.
In reality, the only sure way to get the driveshaft out of the crankshaft is to remove the powerhead and then work on the shaft. Not a fun job.
You can try starting the engine with the lower uint loose but that always seemed dangerous to me.
On the other hand, if the lower unit drops about 1/4 inch, then you need to reach into the gap with a small screwdriver or allen wrench--whichever the screw is-- and remove the screw holding together the upper and lower shift rods.