I can only speak to what I have 1st hand knowledge of.....I have had 3 NAVCON VI Regulators. All three came from E-bay and all were listed as just scuba regulator. The one in the picture is the best of the three. I did take all of them apart and without question there were NO non magnetic parts in any of the three.....I am not saying that there never were any in NAVCON VI's, just the ones I had in my posession. Other than the neat black finish on all parts it's identical to a standard Conshelf VI inside.
The Military regulator in the lower photo is WAY different inside and contains many unique brass/bronze/aluminum parts that are associated with the lo MU stamp on it.
Great Mystery! Keep it up vintage gear detectives!!