About five or so years ago I did this to my `74 Dodge pickup. It had an old and neglected 6-cyl. I didn't go to the extreme that some of the other guys did, but it worked, and yes, the black stuff came out of the exhaust.
Another intresting trick an old man told me was to run some av gas through it. He said that the av gas had the lead in it that the old motor needed. I don't know if it was true, or even if it helped. I did noticed that the truck had a little more power (very small, but it was hard to tell with a slant-6 and 2.76:1 gears), and it made this intresting exhaust smell that I haven't smelled in years.
