I agree with Ralph. I'd be looking everywhere I could to make sure it was a dizzy problem and not something else causing it.
Food for thought, when I first started messing around with BBF's (That's F for "Fords" not "Females"......) I had a couple dizzys around and ran into this little gem on a Comp9000 dizzy that came out of the dissassembled boat I was working on.

Now, both dizzies were for 351C, 400m, 429/460, but why the different gears? Nobody knows. Still have that dizzy, and never seen anything again like it after, but COULD be what you are dealing with..........
Ray