The red line is the cutting line for CF4 bumper which you need to paste it on the S84/86 bumper. But this really need a steady hand to do it. On the other word we still using the original S84/86 bumper but with the CF4 cut on it. Need lots of effort to do it.
But remember once you knock down your bumper you need to standby 2 sets of bumper and of course more $$$ to restore to the same face again.
