The only thing different between the "rifle" encore and the "pistol" encore frames is simply letters on a box. If you buy just a frame it usually comes with the stocks to suit the "letters" on the box, i.e. "rifle" come with rifle stocks, and "pistol" pistol stocks. The barrels are interchangeable. I plan on doing EXACTLY what you are. Buy one frame and purchase barrels to my hearts content.
Brian M.