Did I forget something part 2

So the air coupling was moved from the original position by the propmakers at BBC.

Let's have another look at that.

This is the coupling in its' original place.

The helmet mating surface for the coupling looks like this.

It's actually a flat surface, but with tracks for the locking mechanism. 

The yellow arm thing is the lock, it needs to function with the new placement or the hose may disconnect or tear loose unexpectedly.

I modeled it on the photos above and some measures of the physical parts.
The adapter should look something like this:

This is close enough to do a test print on at least.