You can use the one for the current BT99. It becomes a question of what you want to do with the long tang though. Since I didn't want to cut the tang off in case I ever sold the gun with the original stock I did a bit of reshaping of the tang and then used black electrical tape to hold it to the grip. It looks a bit bubba but most people don't far enough past all of the metal to notice the tape.
epmn