Well, maybe....
Chassis dyno or engine dyno? How much hp did your engine make?
A Roush 427R is basically a Dart block, aluminum heads that flow somewhere around 300 cfm, a hydraulic roller cam, a Victor Jr. intake, and a carb. I do similar combinations all the time and they are always around the 525-550 hp mark. Coincidentally, Roush rates their 427R at 550 hp.
Logically speaking, the displacement is the same, but factory FE head/intake parts are not on the same platform as modern SBF parts, and that's where the difference lies.
Not saying you're wrong, but I think there's a discrepancy somewhere that is being left out. No way a factory 427 will beat a new Roush 427 R (or any 427 Windsor by any manufacturer) by 30-50 hp.