Priobe,
551 HP from 427 ci with 9.0:1 CR. You asked what I think...
My first thought is "yeah right". But I've seen some big numbers in drag race motors from combos you'd not expect to work so well. Mostly those were at 7500 RPM though. You didn't mention RPM, but I'm guessing lower than that, based on 245/250 duration and 112 centers.
My second thought is I recall dyno operators may not include accessories, like alternators, water pumps etc... Also they tend to crank the timing way beyond what you can run reliably when the engine is hot in the engine compartment. Often they will also not use the exhaust that will eventually be used in the car. And on-and on...
I have never been a big fan of dynos except for back-to-back tuning runs, where they can be extremenly beneficial (have done this myself since I use EFI).
I'd be more interested in having you weigh your car; go run the 1/4 mile; then use a horsepower calculator based on mph and let us know what you get. That is really where the rubber meets the road...
Have a nice day
