By the looks of it, there was a "pull tab" at the center lock area. So you would grasp the tab to open. You can see the lighter area of colour on the side leather.
The lining used would of been a irish linen material. The thread sewn with would prob of been a 4 cord irish linen thread. Maybe a 5 cord but most times were sewed 4 cord. Barbour irish linen thread was the main supplier/type of thread used back then. What colour is the thread? White or yellow were the main colours used on bags from that era... but back then barbours came in yellow,white,brown,black, were the main colours. But i have balls of thread in yellow,white,cream,brown,black,light blue,green,red,orange,grey,navy.....
There is the yellow or tan that prob would of used back then. Needed to be run through a wax pot on machines when being sewed... Hand sewing you need to use beeswax on thread.
Depends how far you want to rebuild it. You can pull completely apart, pull all the thread,restiffen leather,resew it all and put back together. Or restitch areas that need to be restitched, Brasso will make the locks shine again if you want that.