The cable routing is OK. But you might think about using a pulley and a fulcrum stop for the cable at the front of the bike. You have less cable resistance so the hub shifts better. You can often find the fulcrum stops and the pulleys at donation LBSs.
Tradition is that the pulley is then mounted just below the seat. With a BSA-badged frame that is how I would do it. They ride a lot better that way