This is getting interesting. After I removed one of the timber lid strengthening pieces (heavily affected by wood rot & filled), and a large portion of the canvas cover, I made a discovery about what I thought were nails helping hold the brackets on. They aren't nails, that's for sure. There is a corresponding, but larger, flat section on the back of them. They must be original, because the canvas surely has never been off before, and these sit beneath that canvas layer. For some bizarre reason they must have chosen to use these in manufacture. Take a look for yourselves.
First photo is the top side of box lid, after canvas stripped back. You can clearly see five round metal surfaces.
Those correspond to two in each lid hinge, and one at rear of the latch. What a lot of effort when screws would have done fine. Especially if the ones I've been trying to get out are anything to go by! Now I'm in a dilema. I cannot simply slap the hinges back down on the....whatever they are, and I don't want to obliterate them. Might have to sleep on that.
Another curious component is the box corner braces. This too is an odd design. I guess they must have had good reason to stamp them with a raised portion to take countersunk screws, but damned if I know it. The simple brackets on my tool box would have been easier to make surely? The metal is noticably thinner on this box, so maybe the stamped (or perhaps embossed would be a better description) surface is to compensate for reduced overall bracket thickness, which would be too thin for rebate to take the countersunk screws!