Hi Allan,
This M4A1 version was built by the Americans and only Americans. That's why it is painted in olive drab and not bronze green.
The production of British DD was too slow before the D-Day, so Uncle Sam gave some copies from his own production.
I don't know any pictures with another gun mantlet like this large one.
The british made the convertion only on the Mark V (M4A4).
And then, there are some pictures with the small mantlet...
Hope i have given you a correct answer.