Nourish. This very forum has a literature section and in there you will find parts lists and catalogues relating to early models. A little perseverance through the early pre-1950 parts list will bring up illustrations of the various toolboxes of the time. These catalogues cover all models, so are a bit less straightforward to use, but the parts are well illustrated, so very useful when researching what a part looks like. If anything, more detailed than the later publications.
Bit late now as you have a good picture of a genuine 1947 rigid toolbox. A modern one to consider is from an Enfield Bullet, which still still has the triangular profile, and might well be easily adapted fit your frame.
Plunger toolbox is bigger, more square and will not fit into the rigid frame, but triangular rigid type boxes appear on early plunger bikes, presumably to use up available rigid stock. Look a bit weird, with a gap underneath to the lower chainstay.
Toolbox lids come with slight variations..... early ones are flat, with a sharp edge, or a later, more domed pressing.
Swarfy.
Additional. This subject has been featured before on the forum, so a search should bring up a few more comments.
