Does anyone know how far a headtube needs to extend above and below the top tube and downtube junction in order to have space to install an external headset cup? I would like to shorten these extensions as much as possible but don't want to find that I can't install the headset cup because, for example, the bulging bottom cup collides with the downtube.
Headset will be Chris King external (technically external/internal--Inset 7). Headtube angle is 73.5 degrees.
Am I missing any other reason that the headtube needs to extend further?