Installing a pitless adapter

I have a new well. It has a 6" steel casing and a 4" PVC sleeve with the space filled with material. Thus, I'm clueless as to how to install the pitless adapter since almost all drawings show it attached to the steel casing.

Drawing on how to installed on this web site

http://www.merrillmfg.com/about/installation/products/02-PitlessUnits/PitlessAdapter.htm