[veltro]

Sorry Franck, but I don't think those are MK 108 structures, or for any other weapon.

IMHO, the "mouth" of the structure is far too smooth and devoid of any visible support to receive a bolted-on part to let us think that a barrel and its cap could be placed there.

Also, the shape of the structure extends also above the wing, whereas the mock-up of the MK 108 nacelle is protuding only below the wing.

Last but not least, the whole frontal part of the mock-up seems to me a lot rounder.

This for why it doesn't seems a weapon to me; to determine what it could be it's all another matter... my wild guess is that those could be aerodinamic enclosures for photo or cine cameras.

Always IMHO, of course.