Since I have my car apart and we're at a stage in the rebuild where I'm waiting for parts, I'm going to photo document some of the lower crossmember/bumper construction on my car. The construction material is aluminum. Thickness is unknown, but seems at least 1/8" wall or so based on weight.
There are two key structural fabricated tubes which serve several purposes. These two items are essential when doing an Audisport setup for the front of the car. They allow for very large front mounted intercoolers and oil coolers as well as audisport front bumper. The upper tube attaches to the front face of the frame of the car with 4 bolts on a flange. The tube is C shaped and nearly horizontal with the ground and is the primary front engine protection. It supports the front snub mount for the engine. It also has two mounting blocks for a front light array. When using all 6 lights, the total weight is probably around 30 lbs. The upper tube has a clip and a female threaded block to hold the intercooler and oil cooler. The upper tube also has extension which go down and back to bolt to the lower tube. The entire upper tube assembly is welded and the pipe is bent or crushed.
The lower tube acts as a brace to triangulate the upper tube. it supports the skidplate and has mounting points for the leading arms which go back to the wishbones of the suspension. Its all just welded up and painted white. While I have mine off, I'm going to clean it up and give it a fresh coat of paint.
Here's where we're at on the motor rebuild. Thats a 3b head in there now just sitting on the block as we work on the wiring harness. See the bank of coilpacks by the firewall. The small AC system is gone. The RR head is at the machine shop getting 4 more exhaust manifold studs added. Yeah! a full 20 studs for a 5 cylinder motor. The wiring in the car is really really good. Its slow going because the compactness and tidyness of the wiring behind the dash makes tracing wires very difficult. In the picture above, there's a really good shot of the funky left side motor mount and custom frame extension to carry it.