Funny you should ask....I had the same question myself, so I tried it.
They will fit, but the only thing holding them in place will be the pin near the bottom and the frame cut at the very top. I am reasonably sure that if you fired it very much the stocks would start to shatter.
I like the feel of the stock target stocks much better than either the Hogue rubber grips or the factory combats. I am going to order a set of Eagle grips that duplicate the shape of factory targets, but are made to fit the N frame round butt.
http://www.eaglegrips.com/guns/SW-Rs...red-H010R.html