'63 Dart GT Headers?

If you have manual steering, then the Clifford shorties will fit - you might or might not get them right away if you order them from Clifford (they have a not so good reputation!). Another option would be dual Dutra duals - I guess you could call them cast iron mini-headers. Member Waggin used to fabricate a set of manifolds that were the front and rear 3 - don't know if he does it anymore though.

If you have power steering, then the only headers that will fit without modifications are the long obsolete Clifford long tubes. An Aussie outfit looks to be remaking them - pretty price with the shipping. The same other options as above still would apply if you have PS.

Another option would be to install a 2.25 inch headpipe allowing the engine to breath a bit better for a bit more performance. Good luck on whatever you decide!