I've made 2 cable backed bows. It was a long time ago, so don't remember the details of them, like dimensions. One exploded, the other survived. But in both cases I added the cable after the bows were tillered. The one that broke, I probably tightened the cable way too much, actually induced a little reflex in the bow, and was re-tillering when it broke. Not sure what I did wrong or it may have been tillering issues before I even backed it with the cable. I would like to try and make another. Keep us posted if you work on another, I will too.
Tattoo Dave