From what I can see they are mild/aluminized steel. 2.5" piping about 24" on the longer part and 10" on the shorter part. They are NOT as bad as the picture makes them out to be but they do have some surface rust. It almost looks as if it is from a header kit but who knows.
The first two pictures are a few random pieces and what appears to be VERY large collectors going to a 5" pipe!

**edit** Keep in mind they have about 20 million years worth of dust on them. you can REALLY see it in the collectors!
Any ideas?