1975-1979 240/260 owners will need to check which brand rear calipers your car is equipped with. The included pads only work with ATE branded calipers.
There is no way to know for sure what calipers are on your car without visual inspection. It is very common on these older cars for the original calipers to have been replaced by a different brand. We've even seen cars with mismatched left and right branded calipers (which take different pads).