The anchoring was one of the reasons I suggested a 4 post lift. it takes much more than 4" to safely anchor a 2 post, I beleive the floor in our shop is something like about 2' thick where the lifts are bolted down. Another thing you have to look out for is getting one that can be set to lift a truck, especially one with the rear kickup in the frame. If you have the right adapters, and know where and how to set it up, they are perfectly safe.
With a 4 post, you don't have to worry so much about lift points, and they can be surface mounted with far less worry about anchoring. Some are even made to be mobile (Backyard Buddy). With a 4 post, you definetly would want to get the dual bridge jack option.
