You must advise exactly which engine you have. The data plate will show this. Also need the transmission ratio. Again the data plate will show this.
The information on the Morgan is readily available (27'6" waterline, 14,500 Lbs) but we need the HP @ RPM and reduction ratio. With this info I can work out a prop calc for you. The prop should be sized for the particular engine/ transmission/ boat combination.
Marine Diesel Engine Vendor