V type
John,
P and Q designations were used to describe the size of the face piece.
You refer to the Harrier. The top photo looks like the type of fitting that was on the end of the mask hose (the green one about 1" diameter)
The Harrier and Jaguar used a man mounted regulator known as a Type 317A or more modern 417A these fitted to some key hole slots on the breast plate on the LSJ.
Does the fitting carry a small tube up the middle? (Known as a compensator tube)
The masks used were V9 and V10 with hooks to connect to the helmet one was size P the other size Q. A mod was introduced to have mask Quick Release (MQR) fittings to the helmet. These were designated Type V11 and V12.
Meggitt made the regulators. I think their designation was MR20 (but that may have been the man mounted regulator we used on the Nimrod. I cant remember if it had just the Air Mix without the pressure breathing - 1.5" WG mask cavity pressure.
I hope you don't intend to use this mask for real without getting someone qualified to check it out on a proper rig.
There was a time when Loadmasters on the Herc required two types. One to hook up to the standard aircraft system and these Walk around bottles described above. And a second V type used on a supplementary O2 system we used at high altitude with the doors open where they used a Jaguar/Harrier type 417A or a 417F without the airmix. We were also developing a "H" regulator which had airmix. this was based on the MR20 and was not duplex as the A and F models were.