I am having trouble putting lower unit back together on my 1973 mercury 850 after repairing water pump. I did not think I would let the splines move for the shifter but maybe something moved and I did not see. But I cannot tell if the drive shaft is hitting first or the shifter splines. Is there a procedure I can use to get shifter in the correct position? It feels like the drive shaft is hitting first but I keep turning the flywheel and cannot get it to go. Any help please