Alright, measurements and pictures, at least shows the difference between the 1100GS calipers and the 2004 1150GSA one. The early R1150GS have apparently the same caliper tham the 1100 but I do not know what year the design has changed.
99 R1100GS, calipers brand Brembo, mounting points 110 mm apart.
04 R1150GSA, calipers brand Tokico (stamped on the back), BMW on the front, mounting points 65 mm apart.
I have a lonely GSA fork apart cause I put a Leading link on the bike for sidecar use