Spitfire Headers Length,What to do??

I,m putting the Spitfire headers in my 66 Dart and am stuck on wether to run my exhaust from the header flanges,or add an extension peice to clear by the torsion bars and stop under my feet?Then run the exhaust from there back.I want to be able to undo and run open headers at the track.Any advise?What have other guys running these headers done?Thanks