Hi,
my personal experience is that they never have the length you want. So custom is the only way...
I use an Odyssey GTX steel Gyro and the built in screws instead of Knarps. This works fine for me since years. I do not know how good it would work with the aluminium version (I doubt that one could tighten the bolts enough) and pretty much all other Gyros do not have these screws at all which is why I would not use them.
Depending on your lever you may use a Gyro cable and something like a Knarp on the lever side. Most Gyros only accept the small ball ends so it might cause problems to use Knarps because there is too less space to clear the cable ends of the lower cable(s).
Did you think about a dual upper cable? The picture shows what I use: a modified Odyssey Londonmod using one inner cable going through the brake lever. It works good!