RE: ideas needed for broken flex header??
FWIW- on very short headers-I use rigid setup and a thick centering silicone on the aft end of the muffler
On ANY tuned setup --whre there is more than 6" of header -- I weld in flex about 4" of it and NEVER put a bend in the flex. If you operate it with a bend it will fail. the tuned can/muffler must be fully, independently mounted in a compliant fixture of some kind