I made mine up ready to fit when I get to that point, bought my braided line from a V8 supercar (touring car) supply shop. They were very specific about the ID of the brake line indicating that if you don't do it right your clutch will not have the right feel. If no one else has definitive knowledge on this I will measure it up next time I am in the shed. I think it was smaller is better and something about the type of line you use.
Could be all sale talk too, but he seemed to on the money as I had to do brake stuff on my MX bike.
Compbrake in UK supplied me bits too... they are great for sales and support....