Some XR3i's had two bolt strut tops and some RS1600i have single bolts. It all depends on whether the car was made before or after May 1983. The two types are not really interchangable. I think the front springs are the same, but the spring cup was mounted an inch lower on the strut. The rear springs are shorter on the RS.

The anti roll bar is the same regardless of which strut tops the car has. The 16i version is alloy as opposed to the S1 Turbo one which is steel. I couldn't believe the difference it made when I fitted a turbo anti roll bar to my car...