This should be a press fit.

Shell is minimum 1,2mm thick

The small / Large boxes in interchangable as long as you keep the geomitry right.

Small box is organized so that alll parts are in their correct place except the row 5 in picture (they are at the bottom in correct orientation)

Part number is counting from top left to right, for smalll boks:
1-2-3-4-5
6-7-8-9-10
11-12-13-14-15