Looking good Wayne.
Not sure about RN aircraft, but the seat harness shoulder straps on RAF 'low back' Spitfires passed over that bar on the head armour, through a slot (in the armour) behind it, and anchored down inside the rear fuselage, in a similar fashion to that of the 'high back' Spits.
The 'tail' of the 'Y' straps was attached to twin 'Bowden' cables which ran up to the anchor point, with a lock/release attached to it, which was operated by a lever to the right (starboard) side of the seat.
I would assume that the RN aircraft were basically the same.
Also, it's probable that the head armour was painted matt black by this period, like the upper part of the cockpit.