Steve Williams acheived next to nothing in an American ring. His resume is as follows:
He went unpinned for ten years in the USA, which sounds great until you realise that all of his mathes were either tag matches in WCW that he occasionaly lost, with his partner being pinned, matches in indy feds nobody cared about, and a victory over Axl Rotten. As soon as he had any real competition, he lost.
The WWF set up Brawl For All to push him, and then he got knocked out by Bart Gunn, essentially killing his career in the North American majors. He was a powerful guy, don't get me wrong, but Superstar Billy Graham was equally strong, and slightly bigger than Dr. Death.
Graham is from a different era, so people will assume that the ECW environment will be new to him, but they are forgetting that:
a) Steve Williams isn't exactly Raven
b) As Shadowmancer said, he had a bull rope match, and a very close Texas Death Match with Bob Backlund.
That being said, I have seen Williams' work and think that while he hasn't had the lasting impact Graham has on the sport (but who has?), Dr. Death would probably get the job done, essentially because he is the more nimble of two powerful guys. It would be close, as Graham is a tough nut to crack - his one year title reign as a heel in the 1970s proves that - but I just think Williams would beat him in a close match.