As far as externals go, the gun was TM compatible. Now due to the lack of info on the gb, I am not so sure.
Looking through different forums, some say the gb is TM compatible while some others say it was not.
Maybe the earliest Olive Green models were not, but according to the time stamps of other posts, it would suggest that the post 2010 ones seem to be TM spec.
Edit: I took a picture of my shell, and measured an internal dimension as well as the internal of the rear to the external of the front. I can't seem to find any specs/dimensions of gb sizes so maybe you can help me out here.