Hi Peter
Here's a wartime pic of the Bv155 cockpit.
From pictures of the preserved example at Silver Hill, it looks like the pressure cabin was a self-contained unit, with a second skin forming the exterior of the aircraft. The fuselage seems to be partially built around a tubular framework - this is visible in the turbosupercharger compartment.
As regards the head armour, in these pics of the aircraft after capture, it looks like there's an internal plexiglass panel supported by diagonal braces.
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Hope this helps
Rowan