HCC metal is not "weird" metal, it is a standard metal used in a number of modern applications. It can be welded, but the heat from standard welding procedures will cause the molecular structure to become drastically weakened. The situations HCC is used in can't have that kind of weakening. That said, as I mentioned, I do not know if HCC is used in that piece or not. But it would be smart to find out due to its structural and safety importance before deciding to start working on it and worse, driving it afterwards.
Right ANY time your working on structure parts it best to have a pro do it, i am a body man thats what i do, all im saying is there is no need to run around checking , just take it in to a body shop (one stop shopping) why fool around, i have seen things that look fine till You dig into them then its a another story. The way you had it worded was for him to run around checking all kinds of things. His does not look that bad, but you never know. Hes already said thats what hes going to do! Good luck