The bright painted design on these Chinese roast eel tins was in fact the feature that drew me to them in the first place (although it turned out that the contents are delicious - so I had no trouble emptying a supply of tins for this project.
The can opens with a pull-tab, which leaves a sharp and inconvenient inner rim - but this can be removed with an ordinary can opener.
Suitable hinges and clasps for a case like this are widely available - I bought these at a large DIY outlet. Positioning the holes for attaching the fittings can be tricky - but this is easily solved with duct tape - by taping the two halves of the case together in what will be the closed position, then taping the hinges and clasp in place, the holes can be punched in their proper places using a hand awl.
The hinge and clasp can just be riveted to the two cans using pop (blind) rivets - this is much easier and more secure than fiddling around with small nuts and bolts.
Here's a video showing the construction method in detail: