It is not brittle AT ALL!! I used a method similar to yours and it took me a good while to get them out. They are made of what appeared to be thin stainless coated with the stuff cats are made of. I used a sledgehammer and a long rod and beat until it all came out of the other end.
Don't know how you are going to get an airhammer in there but good luck and be careful... I bought another set just to be sure that if I screwed up, I still had something to ride.