That mantle is completely wrong for a churchill, it is flush and has the gun coming right from it without any inset.
Although all the pictures indicate the BT-5 had rivets in the mantle, I think this is in fact a later BT-5 made with a straight casting. Or possibly a Bt-7?
Both are wierd, as AFAIK the thompson was only available to crews with US lend lease tanks. It was sort of "standard equipment" and came with the tanks.