I'd have to see a better resolution pic of what's been posted, but from what I can see, it looks like the handle might be a regular square Mark VI. It can slightly be seen peeking out from the bottom of LaBeouf's hand.
It's definately a MK VI and not a WG. It is easy to distinguish the two without needing to see the grips. Just look at the area in front of the trigger guard. The WG has a flat area that is about an inch long. The MK VI doesn't. Also the cylinder is longer on the WG. From the size and the "ramps" in front of the cylinder it is the larger .455 and not the .38.
Also as a further clarification on the Webley MK series. There was both a .38 MK IV and a .455 MK IV. The two guns were totally different and shared no common parts. The .38 MK IV was significantly smaller than the .455 MK IV version.
The larger bore .455 series started with the MK I and went all the way to the MK VI. The smaller bore .38 series also started with a MK I and ended with the MK IV. Because of the same designations there has always been confusion between the .38 and the .455 models.