The dealer indy said he's done this twice. You need to:
1) cut the existing tailpipe and pull out via the bumper
2) betalink the new bumper piece and wait for it to set. Suggested that you paint it first (if required)
3) then you take the new tail pipe and "feed" it through the bumper/new piece
4) clamp/weld new tail pipe/tips onto exhaust ensuring its all level
5) stand back and enjoy