MORE CONFUSION!!
See this article on the 455HO and the Super Duty:
http://www.highperformancepontiac.com/tech/pon_0505_sd/
Down where the picture of the 455 SD head is-
The round-port SD-455 cylinder heads were similar to those found on the R/A-IV and 455 H.O. engines but with revised intake and exhaust ports for even greater flow.