You guys are great. These were all "maybes" in my plans but I didn't have the engineer/physics background to realize it.
The pump cylinder will be new pipe. The seal will have to be where the tapered portion intersects with the old well casing. The gasket will be like a 2 wide rubber belt pushed up against the old well casing by the weight of the water and Tyvek sleeve. I added a few more things to the diagram to hopefully explain it.