Not all BOV's use the same flange, and you'll also need a wastegate flange if your making the hotside yourself, which will need to be welded in.
Mild steel can sag and weaken after seeing 1400+ temps from the heat, but the reality is it'll probably take 3-4years at least to get cycled enough for that to really happen (assuming its not a daily ). By then, you'll have saved up enough to have one of us fancy-weldin folks to make you a stainless one
