What size pump?
Is the pump set at 640' or is that depth of the well?
What is the drop pipe made of? If it is PVC, or PE, you may not need a pump hoist truck. If it is galvanized you definitely will.
You also need to think seriously about the next time you need the pump pulled which will probably be when you have no water, so cutting off the casing and makin' things look pretty may not be a good idea if then you can't get to the casing to pull the pump... Or you may want to fix the slope so a truck can get to the casing off the driveway or whatever is in front of the retaining wall.
In many areas the distance for the casing above ground is 12".