Olivier,
really interesting to read your words. Are there reports about the transport of "White or Yellow4" to Kassel?
I'm not the He 162 expert, but I think the black colour around the cannons isn't a fact for MK 108. In the He 162 booklet X-planes of the Third Reich (page 72) is a series of the "White or Yellow4" with the unpainted tail, and there the MGs 151 are clear visible on both sides of the plane.
Very funny is the fact that I found a pic in the book showing a Yellow 7, also unpainted tail, and a W.Nr. 120067 painted on the wing!
I think the He 162 stuff is really complicated, because the allied trops mixed and overpainted all aircraftparts they found.
I will try to contact the museum in Canada. Maybe somebody of the restauration team can help me. Interesting are the pics I found here:
http://memorial.flight.free.fr/He162.html
http://memorial.flight.free.fr/He162photo.html
http://memorial.flight.free.fr/He162photo1.html
Cheers, Simon