I believe that it was about the time of the 10-8 that Smith decided to turn all Frames into Round Butt configuration. It is simple enough to add a set of Round to Square Butt Stocks to a gun but I've never seen it done the other way around.

Personally, I think this change was one of their better ideas and is actually something of a 'Step Back in Time' for the Company since the Round Butt existed for many Years and the Square Butt was something of a Special Order rather than the norm. This is well shown in the "Regulation Police" Models where the 'Regulation' part was simply a Round Butt gun with a set of Stocks that made it into a Square Butt.