[tsubaki]

Mounting the cavitation plate level with the bottom of the boat is the starting point.
Drilling the holes in the transom might be better done with the motor contacting the transom and the yoke sitting on the transom and marking the upper bolt holes and the upper portion of the lower slot holes. Initially the yoke sitting on the transom will be too low but this will allow the full range of adjustment possible from down to up.
It's very easy to adjust after the initial mounting, just place a board on the ground below the foot skeg, run the trailer jack stand up till the skeg contacts the wood, loosen the lower bolts that have a slot available, remove the top ones that have fixed hole positions and use the trailer jack stand to raise or lower the front in order to raise or lower the motor.
Don't forget sealant for the bolt holes, 5200 isn't overkill either.