Thanks Dags, I'm with you now.
If you look at the bend/wheel to the rear of the one we are talking about, you can see the bracket (or what ever you call the thing that holds the wheel) there. I think the hull would accomidate the gun breach as well as the 'bracket', albeit with very little free room since assault guns of this type seldom have much traverse. I honestly don't know much about it though - I used pictures of the interior of the Char B1 as my reference for how the gun might be mounted.
Gotta love the Char B1 - what a weird and wonderful design!