It is a combination
Clearance against the bottom of the hull is important, not only because you don't want to hit the hull, but the distance affects performance as well. If you contact one or more of the big prop manufacturers, such as Michigan, they can likely help you out. Another thing you need to know is which direction forward is for that engine. Each prop is specified by size, pitch and rotation (L or R). It sounds like you lost your prop nut to electrolysis. Was the zinc on the shaft still?