"Okay - am looking at some Cam Kennedy Norties here": is there any chance of me seeing some scans or other images of those drawings?

That "small circular thingy" may, for once and in comics rarely, be a twin-hose aqualung regulator, but likely drawn too small: see http://en.wikipedia.org/wiki/Image:Aqualung_old_type.jpg .

But a rebreather would give MUCH longer duration for the same weight of breathing set. en.wikipedia.org/wiki/Rebreather

On the Nort logo, a few times I have seen a letter on the semicircular part. Is that a unit or rank symbol?

Is there any known insignia to distinguish a Nort kapten?

If a Rogue Trooper live-action film was made, the Nort actors would have to breathe. That is why UFO series alien helmets have the black lines on their sides: in the film prop they are slits to let air in for the actor to breathe.