I was looking at Al's very nice website and saw the photos of the adjustable seats on some unidentified owner's fuselage. This is a very, very bad idea.
The seats provide all the torsional stiffness for the fuselage between the aft cabane structure and everythingaft of the seats. They are an integral part of the structure that transfers all sorts ofload conditions. Take a good hard look at the structure and visualize how the load flows if you were to twist it. With the fuselage with the adjustable seats, there's no appreciable stiffness. There's going to be a tremendous amount of stress on the longerons after a snap roll, or even after 4-pointers. I'll bet you'll be able to feel the "springiness" in the aircraft from the rear seat. This setup is just begging for big trouble.
Setup the seats to fit you and whoever will be doing most of the flying with you and weld 'em in! I'm a pretty short guy at 5'6", so I raised the seat frame about an inch and a half.Besides, adding anything adds weight! Don't do it!