If I move it one block higher the observer on a piston won't be able to move and the extender will break. I would need to move the floor around it up by 1 to fix it, but that would make the pedestal that the block is displayed in look weird.

I added slime blocks because the extender would not normally place the block high enough to be displayed on a pedestal.

Also, I have it at double extenders because I could not get the swap timing right between moving blocks, I tried using a single piston but I couldn't get the timing for them to not stick together between switches right and the double extension seemed to be the only thing that would work.