A great deal has been written about the history of the locomotive 'Lion' over the years, much of it by the 'Old Locomotive Committee' ('OLCO'), the locomotive's very own supporters club.
In 1930, the November 14 edition of 'The Engineer' had an interesting article (starting on page 535) which was the subject of an earlier post.
Also in 1930, page 684 of 'Meccano Magazine' had a single-page article on 'Lion' which is reproduced below - click on the article to enlarge it.
The pictures in the article show the actual form of the firebox, which I'd describe as "raised round-top". The wonderful brass cover which is now such a characteristic feature of 'Lion' was actually a bit of artistic license by Crewe during the rebuilding prior to the 1930 celebrations.