Have you ever looked at a picture comparison stock 289 manifolds and the gt/hi po manifolds? Now look at the exhaust manifolds of the 460, they look more like the Hi po ones, with a smoother flow to them. At least this is true with the set I just took off my 460 that came out of 73 lincoln. I did replace mine with Sanderson headers which fit great and don't leak, but if your looking for sound and ease of use, stick with the stock ones.
IMHO
Rod