Owen, thank you for your comment.

To start, you will need to piece together pieces 1, 2, 3, 4 and 5 more or less at once.

1, 2, 4 and 5 can be found at the top of panel C:

Attach these to a piece labelled 12345 at the bottom-left of panel B:

The second 3 piece can be found on the largest piece of panel A, which sits diagonally towards the bottom of the panel.

Hope this helps.