I had to make a new "transom" to mount the motor high enough. The cavitation plate is now level with the bottom of the hull at the front tapering to about an inch below at the back. The bottom of the skeg is 9.5" below the hull.
When dried out here the mudline is just under halfway up the prop. The important thing is that the cooling intake is clear of the mud. I usually have about 3" of keel down if I'm trying to get away a bit early (or back a bit late!) so that if there's anything hard and nasty in the way the iron keel catches it before the £75 prop!