What is being asked is a HUD for the THREE-DIMENSIONAL version of a cockpit. If you add a HUD in plane maker, it ONLY shows in the 2D cockpit.
How do you add a HUD to a 3D cockpit? That is the question.
Even if you build a 3D cockpit (obviously a prerequisite), adding a HUD in plane maker will not show it in the 3D cockpit. So how is it done?