Thanks for the inputI did 12" ape hangers from Biltwell with stock cables on my Classic. It is tight and I wouldn't recommend it necessarily, but they don't hang up at all turning the bars. I am looking to replace them with stainless cables soon though.
The custom has no risers, so you'll need those as well if you upgrade. My classic has 2" risers, I think, so that would be 2+12" for my setup. If you get 2" risers, you should be safe with 10-12" bars - but again, they will be tighter and you may want to route some cables differently to make it work.