Actually, Joe is basically right, with Dockboy. That's the highest number I've heard of on a dyno. Snow White and Elmo haven't dyno'd that I know of.
There is a 7.3 based engine that has gone over 1500, though. Ben Miller's Double Overtime pulling truck powerplant. Not a lot left of the original though, it's been converted to mechanical injection, has two huge turbos, and lots of other work. Rumored cost was $150K, and it's nowhere even close to having the manners needed to use on the street.