I assume you've seen the Tech Pages on BBD, and there has been some discussion (including by me) on FABO. I had a pair of the Hooker fenderwells back in the 80's and they were a big hit: they hit the tires, hit the ground, hit the body.
The Hedman 78030 B-body headers fit but only with the following combo:
B block (383/400);
manual steering box;
mini-starter.
I had to make a small dimple to clear a mini-starter. Don't see any way that the giant original Mopar starter would clear. Word has it that the RobbMc starter works, but they cost more than a stock mini-starter.
I'm not sure if the stock Z-bar will clear or not; I made a hydraulic clutch assembly (using a pull cylinder behind the original fork) and it was one less thing to worry about.
Have you disconnected the mounts and jacked the engine up? You may have to remove the left side torsion bar too.
Keep working at it, the savings will be worth it.
I've got some pics on my Dart page that may help:
http://s1181.photobucket.com/user/DrCharlesMorris/library/Dart?sort=3&page=2