Got any pics? There are different forks that will work with the 10.5" bellhousing. I have a shorter one in my 66. I'm also planning on Doug's Headers eventually, so I would like to know what I'm up against.
Another thing that will give you problems is the fact that one of the header tubes will be too close to the Keisler master cylinder. I saw 65 Cuda at Spring Fling that has a Keisler hydraulic setup with Doug's headers. He had to move the master cylinder over to the left about a half inch or so. I'm planning on using a master cylider that mounts up higher so I don't have that problem.
Good luck!
Lee
1966 Barracuda, 340 4 speed