Yeah, i reckon it was the smaller cannon. I had another look to see if i had photos from different angles, but no. Looking at where the barrel joins the turret is probably the most obvious point of differentiation. It has two flanges that stick out on the side, which matches the smaller cannon.

What i find interesting, is that i never realised the shape of the tank. As it is buried so far down, it was no obvious at all. Thanks for the info and sharing the photos.