core support, grill and lights are needed.
94-98 lights will go into a 88-90 GMT400 with dual sealed beams. I haven't heard of them being used on the square bodies.
The front of a square is flat, and the 88-98 is angled. For the lights to fit right in the opening, the beams of light would cross each other.
I have seen one pic of a square with composites, but it had celebrity headlights. I will try to find it.
Edit, found it:
