I'm in the process of finishing up this Duster project. I used a DC type K frame with the relocated spool mounts. I also used TTI headers and they fit pretty well. The driver side collector tubes rubbed against the pittman arm so I had to put a slight dimple in one spot.
If I was starting over I'd move the engine back another 1/4 inch from where it is. I also would open up the core support another inch for the radiator. Other than that I think it came out okay.