Finally got one!!!!!!

[Downunder Kilt]

Harold, the original 1953 issue cantles had the 5 stud attachment system, The also had the pull up release system with the spring steel and a brass hook (which was attached to the front face of the cantle) They also had white metal rivets attached to the front of the cantle in place of the pressed brass dimples that you have in yours

The second model was the push down release, as is yours and up until Artificer documented one with 5 attachment studs on each face, I had only seen one with four on each face.

A 2A model was also put out that was silver plated (I have not been able to find out the reason for this)

A third model was also issued with with the same release mechanism as No2
but made of thinner brass and with smaller dimples pressed into the front of the cantle

BTW Great pick up mate and the current bag looks in great knick