Like that. The four sides of the firebox are four separate plates, the top is a fifth plate like a massive roasting tin, fitted with the flange upwards so that it can be riveted from the outside hydraulically.
It’s a marvellous engine. Very interesting, sufficiently robust that 5 out of the nine survive, and well capable of performing like a normal 6 horse threshing engine. It’s just not photogenically British, which frankly isn’t much of a problem to the driver.