The good thing about the Excalibur line of crossbows is that most parts are the same for each bow. Also with the parts which are different, if you swap them out with another, then your bow becomes that other model (200 lb exomag - standard riser changed to forward riser becomes Exommax, shooting rails are of different sizes, longer for more powerful bow. ect).

The stocks are all inter changable, the question would be could you get your hands onto a thumbhole stock so you can make the change. Also the limbs are the same for all newer bows.

Hope this helps.