About the Rear bumper reinforcement ( I tried to load photos from the Tech service manual but can't), what kind of material is it made of?

 

It's likely some sort of composite material - plastic, fiberglass, something. BTW, I'm assuming you're talking about the actual structure under the bumper cover that takes the brunt of an impact.

The RX-7 had a similar material for the bumper reinforcement - actually works REALLY well, and is very lightweight.

Dale

 

yeah, that's it. It just has to be removed or modified for the Veilside D1-GT rearbumper to fit.