Thanks, and yes a few others elsewhere have also suggested that it is two tins atop one another. There was a variety of heights available, possibly may have all shared the same base size of near 9 -10 inches, but maybe not a perfect square. I think the round opening on top was the same for all which should be 6 inches.
From a scale model of the Stuart tank, have determine the height of the glacis plate where the tins are located, to be approximately 24 inches. The tins don't appear to reach the full height so am guesstimating that each one is about 10 inches tall.
