316L steel is pretty much the standard in replicas and I don't recall any replica case made of another type of steel, I can generalize and say that any replica seller claiming his replicas to be made out of 904 to be either a bullshitter or scammer!
TC basically source his watches from the same factory which bk used to source his watches from, it used to be called wm9.
BK used an alternative to wm9, as wm9 vanished from replica scenes in 2009, the watches came from Taiwan, thus they're known as TW best.
and you cant get the best sub without searching, so use the search function and start reading.
and btw bk have his own section here: http://www.rwg.cc/forum/196-bks-watch-garage/