The direct answer to your question is I know of ONE satisfied Sanderson DD7 user who has posted here. On F.A.B.O. there are over 20 threads mentioning those headers.
I even went so far as calling them and talking to the contact person mentioned in one thread. The guy (Francisco) told me he had made two sets for the guy in Florida.
Headers just haven't been on my radar lately, I already have a set of Spitfires waiting for my next V8 Dart project.
From my recollection of the chat with Francisco it seems someone just needs to make serious inquiry with the idea of actually ordering twins to the '63-'66 A body headers he made for the guy in Fla. Why not you??