On most of the simulator designs I am familiar with going beyond 180 degrees runs in to problems with the simulator structure limiting the field of view. at minimum you are looking at replacing the BP screen and probably the entire mirror cell assembly. The mounting surface the projectors sit on may need replacing and area of the outside of the sim just aft of the mirror cell may need redesign. going from a 3 to 4 projector system means that you end up with an edge blend right in the middle of the primary field of view which is something I personally would try and avoid.