Sideplate...do you mean the parallelogram plate, or the pulley cage?

If the pulley cage:

The NR cage plates (and for that matter, Rally), though different in geometry from second-gen SR, are interchangeable. Nothing except the cage plates need to be replaced - the threaded stud on the derailer that they fit on is identical throughout, and the spring location is the same as well.

One thing - your SR's parallelogram will swing farther forward then an NR if it is a second-gen. Unless it is a first-gen SR, in which case, the cages will be of identical geometry.

If the outer (or inner) parallelogram plate:

I know that they are replaceable, but I have never done so myself. I believe the SR-style expandable pins can be re-used, but the NR squash-fit are a different story. I don't know any more then this, sorry.

-Kurt