Richie,
Once the engine has been changed out (which mine has) there is little way to ID what it would originally have had, so I am sticking with what it has now, US manufacture. As you said virtually everything with a date is removable and could be considered a consumable part, I just have to go by the majority - 1943. I don't have the Gbox top plate
One person has told me that the chassis were stamped with the vehicle ID, but I haven't had any further detail as to where exactly....
It has the bogies hull support fitted so that means it isn't a very early example, having said that these brackets were introduced in 1941?
The lubricators were only added to the parts book in 1944, so for me that helps back up 1943 or early 1944. I suppose they could have been retrofitted, but they are very neatly installed.