[DeeJ]

Pretty much every 260/Rover 75 V8 has had, or will soon have, the same problem. The Two-Sixties have sold hundreds already as you may know, but they have them made in batches for cost reasons.

I wouldn't worry too much about not doing the springs at the same time as the dampers, since taking the strut leg out and re-fitting is a piece of cake on the 260's. Had both of mine done within an hour. Wouldn't mess around with spring rates if I were you, since the standard ones are available. Top mount/bearings are same as the FWD ZT/R75.
Just remove the 3 top mount nuts and the two lower fitting nuts and bolts and it's free to come out as an assembly. You could remove the damper only by removing the big top nut instead of the rubber mount ones if you want. Mine did not even need spring compressors to remove them from the strut leg; the shaft stroke was enough to release compression on the spring. Don't try that on a FWD ZT!