1969 Dart tire & wheels qustion

First off, Welcome to the board. I love that GTX of yours.

The front will need a short tire to clear the headers. 25 or 26" max.

For the rear I think you may be able to get a 275-60 back there with the offset hangers. Hope I helped alittle.

By the way, Pay no attention to 80s style CenterLines. :D