Unit Part: Hat - Milkshape - Adding a new Plane to existing model help

[Slyk]

I am trying to add a new plane, two triangles, to an existing model. The images below show the in-editor image render which appears to be perfect and then the in-game render of the new plane out of position.

I have welded the four corners of the two-tri plane to the existing model.
I have regrouped LOD0 with the new plane
I exported the model using the NTW plug-ins... (I have successfully edited and got other ACW models working in-game without error.)

From the limited details I have found so far about Milkshape, I think my issue is properly assigning both "Joint" and "Weight" to the vertices.

Can anyone point me to the final steps here to get this element to work correctly? I'll offer a free download of my mod